Using measurements at different angles to characterize the internal structure of a device under test

Abstract

The present invention relates to a method for measuring a target area (35) of a device under test (30), comprising providing a measuring device (10) configured to perform a measurement by emitting a measurement signal along a measurement path (15) and receiving a received portion of the measurement signal; with the measuring device (10), performing a plurality of measurements for a plurality of measurement paths (15), respectively, to thereby obtain a measured data set; wherein for at least some of the measurements the respective measurement paths (15) intersect the target area (35) at different incidence angle The present invention also relates to a system for measuring a target area (35) of a device under test (30).

Description

[0001] Using measurements at different angles to characterize the internal structure of a device under test

[0002] Field

[0003] The present invention generally relates to measuring a device under test, such as, radomes for automotive radars. More particularly, the present invention relates to determining at least one property of a target area of the device under test by utilizing multiple measurements at different incident angles.

[0004] Introduction

[0005] Radars are detection systems or sensors that use electromagnetic waves to determine range, angle or velocity of objects. An emerging technology is the use of radar systems in automotive industry. More particularly, radars operating in high frequencies, such as, 20 to 160 GHz, usually between 70 and 90 GHz, can provide a very high range resolution and achievable accuracy. This feature makes such radars preferable for use in parking assistants, blind spot monitoring, brake assistant systems, etc. However, due to the very high operating frequency, such radar systems can suffer from high signal attenuation.

[0006] A radar is usually set to operate in open-air conditions. Thus, the radar is exposed to different weather conditions, dust or other external particles and forces that may damage the radar and / or lower the accuracy of its measurements. In cars the radars are wanted to be covered for aesthetic reasons so that they are not visible. To alleviate the above, a radome, also referred as a radar dome or radar cover, is implemented around the radar, hence, protecting it against external factors and / or reducing its salience. Typically, the bumper or the emblem of a vehicle is used as a radome to cover and hide the radar.

[0007] While hiding the radar (e.g., behind a bumper or emblem of car) can offer protection to the radar and can decrease its salience, it can also affect the operation of the radar. Due to dielectric characteristics of the radome material, the radome may cause unwanted reflections, attenuation, beam deflection, beam broadening, sidelobe increase, etc. These side effects may introduce errors in the radar sensing. The unwanted effects caused by the radome, particularly attenuation and reflection, can become significant when the radar operates in high frequencies. For example, the radars operating in high frequencies, usually used in automotive industry are highly susceptible to suffer from attenuation and other unwanted effects caused by the radome.

[0008] Thus, in one hand it is advantageous for various reasons (e.g., protection against weather conditions or external elements or forces and / or improving vehicle design) to cover the radar sensor with a radome. On the other hand, the radome can introduce unwanted effects (e.g., signal attenuation and reflections) that may increase the inaccuracy or decrease the detection or sensing capability of the radar.

[0009] Furthermore, the use of radar systems in vehicles, such as for parking assistance, blind spot monitoring, braking assistance, etc., are prone to strict requirements set by legal standards, such that maximum safety can be ensured for traffic participants. These standards or regulations usually require high detection accuracy.

[0010] Determining the layer thickness of a multi-layered target, e.g., a bumper plate used as a radome in front of an automotive radar, can be advantageous however it is a timeconsuming and error-prone process. Such a radome usually consists of several layers, with each having complex-valued permeability, complex-valued permittivity and a thickness. The complete layer stack determines transmission, reflection and absorption of electromagnetic waves in the radar spectrum, which are important properties for advanced radar. More generally, for arbitrary targets knowledge of layer thicknesses can be an important aspect of quality control or useful in R&D tasks.

[0011] Current approaches measure these properties separately and in a destructive fashion. For example, in a first step permittivity of each layer is measured. Then, in a second step, a layered target is destroyed layer by layer, and for each layer the thickness is recorded.

[0012] Some attempts have been made trying to alleviate the shortcomings of using a radome.

[0013] For example, US 5,371,505 A relates to a method for determining signal transmission characteristics for a selected area of a radome.

[0014] US 3,936,736 A relates to a hand-held universal radome tester which is an instrument for locating discontinuities and impurities inside a radome wall and for determining the quality of an anti-static paint coating over the exterior surface of a radome.

[0015] EP 3,258,288 Al relates to a method and system for testing the transmission and reflection properties of a radome.

[0016] US 5,066,921 A relates to a system for testing radomes to detect defects and evaluate the radome effect on antenna patterns.

[0017] EP 3,864,430 Al relates to a radome measuring system comprising a clamp structure.

[0018] WO 2022 / 063794 Al relates to a method of measuring a property of a radome. Pfeiffer, F. (2009). Analyse und Optimierung von Radomen fur automobile Radarsensoren. Munchen: Technische Universitat Munchen. pages 29-31, retrieved from: herein after referred to as Pfeiffer,

[0019] F. (2009) derives analytical expressions of the reflection and transmission coefficients for a wave incident on a layer stack.

[0020] Summary

[0021] The present invention relates to a method for measuring a target area of a device under test. The method comprises providing a measuring device configured to perform a measurement by emitting a measurement signal along a measurement path and receiving a received portion of the measurement signal. The method further comprises with the measuring device, performing a plurality of measurements for a plurality of measurement paths, respectively, to thereby obtain a measured data set. For at least some of the measurements the respective measurement paths intersect the target area at different incidence angles.

[0022] A main idea underlying the present invention can be that a set of parameters, such as the layer thicknesses, the layer complex permeability and the layer complex permittivity of a radome can be measured in a non-destructive and non-contact way using multiple measurements taken at different angles by either actively producing or passively utilizing such different angles. This can offer enough non-linearity in the measured data and hence information to simultaneously optimize for multiple parameters.

[0023] Optimization may require solving a non-linear inverse problem. The preferred method for that can be formulating the problem as a non-linear least squares problem and solving it with second-order methods, such as, Levenberg-Marquardt. It may be advantageous to have a reasonable initial guess on the parameters to optimize for. However, this can be easily satisfied in most applications.

[0024] The hardware configuration can be very flexible. It may only be sufficient to take transmission and / or reflection measurements at different incident angles. The hardware setup that can be used for the present invention can consist of the following parts:

[0025] 1. A measuring device that can comprise at least one transmitting antenna and at least one receiving antenna. Antennas can also be transmitting and receiving, i.e., transceivers. An example could be the Radome Measurement Systems produced by the applicant. 2. A device under test. The target may consist of a layered structure and may be approximately planar.

[0026] 3. Zero or one or multiple positioning units. The positioning unit(s) can be used to move the measuring device and / or the device under test. The positioning unit(s) can take the form of a linear stage, a robot, or any other suitable device capable of adjusting the relative position between the measuring device and the device under test. The positioning unit(s) can also be used to move at least one antenna of the measuring device, i.e., the measuring device itself might incorporate positioning units. Multiple fixed installed antennas can substitute positioning units.

[0027] Any antenna has a specific antenna (gain) profile. Depending on the use case, different antenna profiles may be desirable. The transmit and receive antennas, that can be comprised by the measuring device, can be quite focused in order to measure a small defined area. This may limit edge and corner effects on the measurements, as reflected waves from outside the measurement path can be less powerful and therefore unwanted reflections arising from outside the target area may not influence the measurements as strongly.

[0028] Every antenna may preferably have a known polarization direction. This may be advantageous because polarization and incident angle can both affect the transmission and reflection values of known samples.

[0029] The present invention can measure one or multiple points or areas of a target. Such a point or such an area can be referred herein as target point or target area interchangeably. It will be understood that practically it may not be possible to measure an idealized point. Preferably, the determined properties (described further below) should hold homogenously over the target area.

[0030] The size of the target area can be dependent on the measurement setup, the antenna profiles of the antennas that can be comprised by the measuring device, the relative position between the antennas that can be comprised by the measuring device, the relative position between the target area and the measuring device and / or the incidence angle. For example, in some embodiments, the target area at a 90° incidence angle may be 14x10 millimeters. When the target area is tilted, i.e., when the incidence angle is different from 90°, the target area may be increased, as a larger area of the device under test intersects the volume where transmitted signals will be received by the receiving antenna with a suitably high power.

[0031] Any target area can be approximately formed by stacked flat or planar layers. Each layer material can be characterized by a complex-valued permeability and a complexvalued permittivity. The permeability and permittivity can usually be expressed in form of a real part and a real-valued loss tangent ( tan(<5m)).

[0032] Complex-valued permittivity can be expressed as:

[0033] £ = e0■r= E' + js" = E' ■ (1 — jtan(<5e))

[0034] Complex-valued permeability can be expressed as: jtan(<5m))

[0035] £0and0are the permittivity and permeability of vacuum, respectively, and crand are the relative values referenced to the values of vacuum, E' and / / ' are the real parts of the permittivity and permeability, E" and / / " are the imaginary parts of the permittivity and permeability and tan(<5e), and tan(<5m) are the lost tangents of the permittivity and permeability.

[0036] Typical devices under test measured by the present technology, e.g., automotive radar covers, comprise non-magnetic materials with a relative permeability of 1 for millimeter waves, i.e., waves with a frequency between 30 GHz to 300 GHz. Moreover, layer permittivity can vary between approximately 1 and 100, the layer loss tangent between 0 and 0.1 and the layer thickness between 1 micrometer and 1 centimeter.

[0037] Moreover, it can be assumed, that layer permeability and permittivity can be constant for all frequencies at which the measurements are taken. Furthermore, it can be assumed, that the permittivity is isotropic, which may be necessary if described by a single (complex) number.

[0038] The permeability and permittivity of a material can, however, be anisotropic, which can be the consequence of certain production methods. This is typically undesirable. If, however, axes describing the anisotropic properties may be known, at least partially the present invention can still be used.

[0039] Should the permeability and permittivity for different frequencies differ, it may be advantageous to know the permeabilities and permittivities for each measured frequency. In this case, only optimization for layer thickness may be performed. Usually constant permittivity over an, e.g., 3 GHz bandwidth, e.g., from 75 to 78 GHz, is reasonable assumption. It may further be advantageous for the permittivities of different adjacent layers to differ, as such differences may allow for them to be distinguished between each other. Adjacent layers that have the same permeability and permittivity at all measured frequencies may be indistinguishable from each other, i.e., may be considered as a single layer.

[0040] At each measurement time, at least one measurement path in space may be defined. Each measurement path may be characterized by a transmitting antenna and a receiving antenna, which can be identical. If at one time multiple measurement paths are present, e.g., due to having more than one transmitting and one receiving antenna, it can be advantageous for the measurement signals not to interfere with each other.

[0041] At each measurement time, the target is positioned in a specific way, such that the respective target area intersects the measurement path. The size of the target area may depend, among other things, on the measurement setup, especially the angle between the antennas and the target, the size and profile of the antennas.

[0042] The role of a positioning system and / or of the antenna configurations may therefore be to facilitate measuring the target area from different angles and / or at different measurement times. If this can be assured using multiple antennas, a positioning system may not be required.

[0043] Due to the polarized nature of the antennas, angles can be "two-dimensional". That is, there can be an incidence angle and a polarization angle defining each measurement.

[0044] Each positioning should be done in a way such that the intersection between the device under test and the measuring signal can be part of the target area, as mentioned above.

[0045] Measuring at different angles and optionally at different frequencies may result in data complex enough to solve a highly non-linear optimization problem. The measurements can be performed at any order.

[0046] The measurement process can consist of the following parts:

[0047] • Generate multiple measurement paths by actively inducing or utilizing different relative positionings between the measuring device and the target area and / or by providing a measuring device with multiple antenna pairs.

[0048] • Associate with each measurement path with an incidence angle and a polarization angle.

[0049] Potentially also associate with each measurement path a side from which the target area is measured (then the layer stack may be inverted accordingly). Measure at at least one frequency either transmission or reflection coefficient.

[0050] • Repeat for at least one angle and optionally at least one frequency, but at least generate as many measurements as unknowns to solve for. Preferably, generate a lot more measurements than unknowns.

[0051] The result of the measurement process, i.e., the measured data set, can comprise a collection of transmission and / or reflection measurements, each with the following information:

[0052] • incidence angle,

[0053] • polarization angle,

[0054] • measurement frequency and

[0055] • from which side was the target area measured.

[0056] The processing of the measured data set may comprise solving a non-linear least squares problem. Any of the following target properties may be advantageous to reduce the optimization task complexity:

[0057] • whether the target has isotropic properties;

[0058] • bounds or approximate values on the number of layers comprised by the target area;

[0059] • bounds or approximate values on at least one thickness of a layer comprised by the target area;

[0060] • bounds or approximate values on at least one (complex) permittivity of at least layer comprised by the target area, e.g., in the form of bounds or approximate values on the (real) permittivity and / or the loss tangent;

[0061] • bounds or approximate values on at least one (complex) permeability of at least one layer comprised by the target area, e.g., in the form of bounds or approximate values on the (real) permeability and / or the loss tangent.

[0062] Each measurement produces a (complex) value. How reflection and transmission values are calculated is secondary to this invention. For any possible target area, the correct transmission and / or reflection values given the respective layer-properties of each layer comprised by the target area can be calculated theoretically. Analytical expressions of the reflection and transmission coefficients can be derived for a plane-wave incident on infinitely expanded planar layer configuration with isotropic materials - see Pfeiffer, F. (2009).

[0063] The present invention may optimize the layer-parameters of the target area given the measured transmission and / or reflection values. The optimization algorithm may utilize an iterative approach. Because of the inherent non-linearity and complexity of the problem, in order to achieve a good solution, it may be advantageous to have initial layer-parameter estimates.

[0064] Theoretically, any layer stack configuration can be associated with a quality of fit, using a loss function. Optimization algorithms, like Levenberg-Marquardt, can be a way of finding a local minimum of the loss function. The problem itself can have multiple solutions with a good quality of fit. For example, the loss function can have multiple local minima and one global minimum. Successful optimization can rely on initial layer-parameter estimates and measurement accuracy.

[0065] The quantity of measurements necessary to achieve an acceptable result may depend on the accuracy of the measurements, the properties of the target (e.g., similar permittivities are hard to distinguish) and the accuracy of the initial values for the layer-parameters.

[0066] It can be advantageous to fix certain known layer parameters and optimize only over the remaining parameters. This can simplify the problem.

[0067] The most advantageous knowledge may be the number of layers. This is in fact may be implicitly necessary because initial values for the layer stack configuration are required. However, it may also be possible to specify multiple initial value estimates for configurations with a differing number of layers, then optimize each layer and then choose the solution which fits the data best.

[0068] Present invention may allow for thickness estimation of intermediate layers and especially of multiple layers, in a non-destructive and accurate manner.

[0069] Modern radar sensors suffer from angle defects, which can arise from the differences in transmission values that arise from different incident angles. Knowledge of the full layer stack could be used to account for these errors and thereby improve radar calibration.

[0070] In a development environment, the invention could be used to lower development cycle times in material design and production design. For example, a producer of machinery used to coat bumpers might be interested to lower the average thickness of the coating without compromising the visually perceived color, as on a large scale this will lower mate- rial consumption significantly. The invention could significantly speed up development cycles, as it would allow to quickly test how consistently a certain thickness of paint can be applied. In this case, there is no immediate connection to radar, but the invention would still be useful.

[0071] With the complete knowledge of the layer stack (material and thickness properties of each layer), reflection and transmission values can be calculated for any incident angle, polarization, and frequency. These values can then be used for a quality control of parts without the necessity to measure all configurations. Especially an angle dependent reflection measurement is very difficult to conduct as it requires a bistatic antenna configuration of the transmit and receive antenna to "catch" the reflected wave at the angle of reflection (angle of incidence is equal to angle of reflection.

[0072] In a first aspect, the present invention relates to a method for measuring a target area of a device under test. The method comprises providing a measuring device configured to perform a measurement by emitting a measurement signal along a measurement path and receiving a received portion of the measurement signal. The method further comprises performing, with the measuring device, a plurality of measurements for a plurality of measurement paths, respectively, to thereby obtain a measured data set. For at least some of the measurements, the respective measurement paths intersect the target area at different incidence angles.

[0073] Throughout the specification the terms "incidence angle" and "angle of incidence" are used interchangeably.

[0074] The present invention can thus enable a property of the target area to be determined. The property may be an electromagnetic property of the target area describing how an electromagnetic wave incident on the target area can be affected by the target area. For example, the electromagnetic property can be a transmission and / or reflection property of the target area. As is known in the art, such properties typically depend on the frequency, angle of incidence and polarization of the incident electromagnetic wave. By performing measurements with different angles of incidence, the present invention may enable a diverse set of measurement data to be obtained, thereby enabling the determination of multiple unknown electromagnetic properties.

[0075] In the simplest scenario, where the target area comprises a single layered structure, a measurement via a single measurement path intersecting the target area at a particular angle of incidence may be sufficient - at least ideally. For example, if a transmission coefficient of the target area is to be determined, and given that the target area in this scenario consists of a single layer, there can be a single unknown to solve for. Therefore, a transmission measurement over a single measurement path may allow the transmission coefficient to be determined. Similarly, if a reflection coefficient of the target area is to be determined, and given that the target area in this scenario consists of a single layer, there can be a single unknown to solve for. Thus, a reflection measurement over a single measurement path may allow the transmission coefficient to be determined.

[0076] However, the present invention is particularly advantageous in scenarios where the target area comprises multiple layers. With a multi-layered target area, there may be multiple unknowns corresponding to the electromagnetic properties of each layer. Therefore, it may not be sufficient to perform measurements at the same angle, given that there are multiple unknowns. However, according to the present invention, it may be possible to estimate a respective layer property for each layer by performing several measurements with different angles of incidence.

[0077] It is noted herein that a similar but inferior effect can be achieved by performing measurements at different frequencies and / or with different polarisations. However, since there are only two polarisations, at most two unknowns can be determined by performing only measurements with different polarisations. On the other hand, frequency variations are also limited because the DUT typically needs to be measured for a specific frequency range. Therefore, the use of angle of incidence variations can be particularly advantageous for obtaining a diverse measurement data set.

[0078] The different incidence angles can be within a range. That is, there can be a minimum and a maximum incidence angle defining said range. It will be understood that the larger the range, the larger the variety of the different incidence angles can be. However, there can be can be limits on how much the incidence angle can vary. That is, there can be limits on how large said range can be. With increasing incidence angle, the surface of the target area can also increase. Thus, when a property of the target area can be determined, it is averaged over a larger area. This averaging may diminish measurement quality. Additionally or alternatively, the measuring device and the DUT may need to move relative to each other to realize the different incidence angles. Depending on size and shape of the measuring device and / or of the DUT this may only possible within a certain range of incidence angles.

[0079] Thus, the different incidence angles can be within a range and said range can be dependent on the size and shape of the measurement device and / or the device under test.

[0080] Alternatively or additionally, the different incidence angles can be within a range and said range can be dependent on an expected measurement accuracy. The difference incidence angle can be between -60° and 60°, preferably between -15° and 15°.

[0081] The method can comprise performing at least some of the plurality of measurements with a time-delay between each other. That is, the method may comprise conducting a portion of the numerous measurements with a time gap between them. In other words, some measurements may have intervals of time introduced between them. This approach can be beneficial for reducing interference between the measurements, even if all measurements employ the same frequency. As a result, it can be possible to perform measurements at the identical frequency. Further still, with this approach it can be sufficient for the measuring device to comprise a single antenna pair. The duration of the time gap can be chosen in a manner that causes the measurement signals and any reflections to decrease in intensity below a predefined threshold, for example, to the point where they have a negligible impact.

[0082] The method can comprise performing at least some of the plurality of measurements simultaneously or quasi-simultaneously. In this context, measurements executed with an extremely short time delay, potentially caused by electronic circuitry, are considered quasi- simultaneous. That is, the method can comprise performing some or all of the multiple measurements either simultaneously or in a nearly simultaneous manner. This simultaneous or quasi-simultaneous approach may allow for a rapid measurement of the target area. However, it should be noted that this approach may be vulnerable to interference. Therefore, it may be beneficial to implement interference mitigation mechanisms.

[0083] The measuring device can comprise at least one antenna pair, wherein each antenna pair can comprise a transmitter and a receiver, and wherein each antenna pair defines a respective measurement path. The antennas within each antenna pair can be operated in coordination, enabling a signal transmitted by one antenna of the pair to be received by the other antenna within that same pair. Consequently, the antennas in each pair can be aligned with one another to facilitate this coordinated operation.

[0084] The measuring device can be configured such that a single antenna pair can be utilized to perform the plurality of measurements. This configuration may lead to a simpler, more compact antenna setup that requires less maintenance. Moreover, it can eliminate the potential variability associated with multiple antenna pairs, such as differing misalignments, differing antenna characteristics, and differing calibrations. These variations can introduce inaccuracies in the measurement of the target area. In summary, a measuring device equipped with a single antenna pair can offer advantages in terms of reduced complexity, compactness, and improved measurement accuracy.

[0085] The measuring device can be configured such that at any instant of time a single measurement path can be defined. This can be the case, for example, if the measuring device comprises or utilizes a single antenna pair for measuring the target area.

[0086] The method can comprise generating a relative motion between the measuring device and the target area to define at least some of the measurement paths that intersect the target area at different incidence angles. That is, the method may involve inducing relative motion between the measuring device and the target area, effectively establishing various measurement paths that intersect the target area from different incidence angles. This capability may allow for the generation of numerous incidence angles, thereby facilitating the creation of a diverse measurement dataset. This, in turn, expands the scope and range of available incidence angles for the measurements.

[0087] The method can comprise performing at least some of the plurality of measurements during the relative motion. Put differently, the method can comprise conducting at least some of the multiple measurements while the relative motion is ongoing. This approach can offer the advantage of enabling continuous motion, eliminating the need for motion pauses during which measurements would be taken. Consequently, the measurement dataset can be acquired more rapidly. Additionally, measuring during the relative motion may enhance the probability of capturing measurements along paths that intersect the target area at varying incidence angles, thereby providing a diverse measurement dataset.

[0088] In some embodiments, the relative motion can comprise a rotational motion of the measuring device and / or of the target area. Rotational motion can be advantageous as it can guarantee the variation of the incidence angle, contributing to the diversity of the measurements.

[0089] In some embodiments, the measuring device can comprise a plurality of antenna pairs, respectively defining at least some of the measurement paths that intersect the target area at different incidence angles. This configuration may enable the simultaneous or quasi-simultaneous execution of multiple measurements, leading to a more rapid measurement process. Furthermore, if relative motion is employed to generate additional incidence angles, a reduced range of motion may be necessary.

[0090] In such embodiments, wherein the measuring device can comprise a plurality of antenna pairs, respectively defining at least some of the measurement paths that intersect the target area at different incidence angles, the method can comprise performing at least some of the plurality of measurements with different antenna pairs.

[0091] In such embodiments, wherein the measuring device can comprise a plurality of antenna pairs, respectively defining at least some of the measurement paths that intersect the target area at different incidence angles, the method can comprise performing at least some of the plurality of measurements by utilizing at least two of the antenna pairs simultaneously or quasi-simultaneously.

[0092] The method can comprise performing at least some of the plurality of measurements by utilizing at least two of the antenna pairs at different frequencies. This configuration may enable the simultaneous or quasi-simultaneous execution of multiple measurements, leading to a more rapid measurement process, while decreasing potential interference between the antenna pairs.

[0093] The method can comprise performing at least some of the plurality of measurements by utilizing at least two of the antenna pairs at different time intervals. This configuration decreases potential interference between the antenna pairs.

[0094] In some embodiments the measuring device can be configured such that at an instant of time multiple measurement paths intersecting the target area at different incidence angles can be defined. This configuration may enable the simultaneous or quasi-simultaneous execution of multiple measurements, leading to a more rapid measurement process.

[0095] The target area can comprise multiple layers stacked on top of each other. As previously discussed, the present technology is particularly advantageous for such multi-layered target areas because it may allow the determination of properties for each, or at least some, of the individual layers. In addition, the devices under test (DUTs) that are typically measured using this technology are often multi-layered. For instance, a typical DUT might consist of one or more substrate layers, together with one or more ink layers and one or more coating layers stacked on top of each other. An illustrative example of such a DUT would be a vehicle bumper or emblem that functions as a radome for vehicle radar systems.

[0096] The method can comprise, with a data processing system, determining at least one layerparameter of the target area based on the measured data set. That is, the present technology may enable a more accurate and exact measurement of the target area. Unlike certain existing technologies that primarily determine an overall or effective property of the target area, the present invention may allow characterizing individual layers within the target area. Importantly, these measurements are conducted without causing any damage to the target area, ensuring a non-destructive assessment.

[0097] In some embodiments each layer-parameter can be indicative of a layer-property of the target area. That is, the layer-parameters determined by the present invention can provide insights into the layers of the target area.

[0098] In some embodiments one layer-parameter can be indicative of a number of layers of the target area. That is, the present invention may enable the determination of the layer count within the target area. This capability can prove valuable in verifying the structural integrity and manufacturing quality of the target area. For instance, it can be used to detect whether the target area is missing a layer, thereby ensuring the proper composition of the target area.

[0099] In some embodiments one layer-parameter can be indicative of a respective layer thickness of at least one layer of the target area. That is, the present invention may allow determining the thickness of one or more layers of the target area. This capability provided by the present invention can be valuable because, in many cases, the thickness of layers may be unknown and / or may not be precisely controlled during the manufacturing process. As a result, the ability to determine layer thickness is highly advantageous for assessing and ensuring the quality of the DUT's manufacturing process.

[0100] In some embodiments one layer-parameter can be indicative of a respective layer electromagnetic property of at least one layer of the target area. Therefore, the present technology may allow determining one or more effects that one or more layers of the target area respectively have on electromagnetic waves. In turn, this can increase the accuracy of determining an overall effect that the target area can have on an electromagnetic wave. This is particularly advantageous if the device under test is used as a radome.

[0101] In some embodiments the respective layer electromagnetic property of a layer can be indicative of a permeability of said layer. That is, the present technology may enable the determination of one or more permeability values associated with the individual layers within the target area.

[0102] In some embodiments the respective layer electromagnetic property of a layer can be indicative of a permittivity of said layer. In this context, the present technology may allow for the determination of one or more permittivity values associated with the individual layers comprising the target area. In some embodiments, determining at least one layer-parameter of the target area can comprise determining a plurality of layer-parameters of the target area simultaneously. That is, rather than determining layer-parameters one after the other in a sequential manner, they can be determined simultaneously. This simultaneous approach may allow for concurrent optimization, leading to more accurate results.

[0103] In some embodiments at least some of the layer-parameters of the target area correspond to different layers of the target area. That is, several layers of the target area may be characterized.

[0104] The method can comprise determining the plurality of layer-parameters of the target area simultaneously by simultaneously optimizing the plurality of layer-parameters. Simultaneous optimization may offer several advantages. Firstly, it can aid in the discovery of global optima, increasing the likelihood that the best solution is found and that local suboptimal solutions are bypassed. This may lead to results that are not only accurate but also highly effective. Secondly, it can enhance efficiency by simultaneously considering multiple layer-parameters. Lastly, multiple interdependent layer-parameters can be optimized together.

[0105] In some embodiments the plurality of layer-parameters of the target area can be indicative of a layer thickness and of a layer electromagnetic property of each one of at least some of the layers of the target area. That is, the numerous layer-parameters that may be determined by the present invention, may provide information about both the thickness and electromagnetic properties of individual layers of the target area. This information can be especially valuable when the DUT is intended to function as an antenna cover in general and in particular as a radar cover, also known as a radome.

[0106] In some embodiments the plurality of layer-parameters of the target area can be indicative of a layer thickness, of a layer permeability and of a layer permittivity of each one of at least some of the layers of the target area. Again, this information can be especially valuable when the DUT is intended to function as an antenna cover in general and in particular as a radar cover, also known as a radome. Thickness, permeability and permittivity can be important parameters to know for an antenna or radar cover because they can directly influence how electromagnetic waves, such as radar signals, interact with the material of the DUT. In this context, knowing the permeability and permittivity of each layer can provide more insights on how the DUT affects electromagnetic waves.

[0107] The method can comprise with a data processing system, determining at least one target area parameter, wherein each target area parameter can be indicative of an end-to-end property of the target area. The end-to-end property of the target are can also be referred to as an overall property of effective property. It can be indicative of an overall or effective effect that the target area can have on electromagnetic waves incident on the target area. Typically, the end-to-end property of the target area can be beneficial to know for testing the DUT and / or for generating calibrating parameters associated with the DUT. The calibrating parameters can be beneficial if the DUT is used as an antenna cover, e.g., as a radome, wherein the calibrating parameters can be used to calibrated the covered antenna or radar to compensate for the effects of the DUT on electromagnetic waves.

[0108] The method can comprise determining the at least one target area parameter based on the measured data set. This can be done, for example, based on the measurement signal as emitted and based on the received portion of the measurement signal. For example, the received portion of the measurement signal may comprise a transmitted portion which is a portion of the measurement signal that has propagated through the target area before being received. A transmission coefficient can be calculated as a function of the transmitted portion of the measurement signal as emitted. Similarly, a reflection coefficient can be calculated but instead using a reflected portion of the measurement signal. Using the transmission and / or reflection coefficients other parameters of the target area can be derived such as permittivity, permeability and / or thickness.

[0109] The method can comprise determining the at least one target area parameter based on the at least one I a yer- para meter. That is, first one or more layers of the target area can be characterized. For example, a layer thickness, layer permeability and / or layer permittivity of at least one layer, preferably of each layer, can be determined. Then, based thereon the target are parameter can be determined as a function of the at least one layerparameter. An example of such a function is described in Pfeiffer, F. (2009).

[0110] In some embodiments one target area parameter can be indicative of an end-to-end thickness of the target area.

[0111] In some embodiments one target area parameter can be indicative of an end-to-end electromagnetic property of the target area.

[0112] In some embodiments the end-to-end electromagnetic property of the target area can be indicative of an end-to-end permeability of the target area.

[0113] In some embodiments the end-to-end electromagnetic property of the target area can be indicative of an end-to-end permittivity of the target area.

[0114] In some embodiments, the method can comprise obtaining, using a data processing device and from a memory, a computer model of the target area. The computer model can comprise model parameters indicative of layer properties of the target area. The computer model can be configured to digitally replicate a measurement by receiving as input data indicative of a measurement signal incident on the target area and calculate an output indicative of an expected received portion of the measurement signal. In such embodiments, the method can further comprise determining the at least one layerparameter based on the computer model.

[0115] That is, the computer model can replicate effects that the target area can have on incident electromagnetic waves. For example, the computer model can be an analytical model based on electromagnetic wave propagation principles and Maxwell's equations. It can comprise a set of equations able to calculate the expected received portion of the measurement signal directly or indirectly by calculating one or more parameters that can be indicative of the expected received portion of the measurement signal. Said one or more parameters can for example comprise a transmission coefficient and / or a reflection coefficient.

[0116] The output of the computer model can be indicative of an expected measured data set. That is, the output of the computer model can indicate the measured data set that would have been measured during a measurement if the measurement signal characterized by the input data. The output of the computer model can be directly or indirectly indicative of the expected measured data set. For example, the output of the computer model can be directly indicative of the expected measured data set by comprising the expected measured data set. Alternatively, they can be indirectly indicative of the expected measured data set by comprising data that can allow deriving the expected measured data set.

[0117] The input to the computer model can be configured to characterize, at least in part, the measurement signal incident on the target area. In some embodiments, the input to the computer model can be configured to fully characterize the measurement signal incident on the target area. For example, the input to the computer model can comprise a frequency, an amplitude, a polarization and / or an incidence angle of the measurement signal. Typically, these data are known as they correspond to the measurement setup.

[0118] The model parameters can comprise information related to layer properties of the target area. That is, the model parameters can be descriptive of the target area and in particular of the layers of the target area. Preferably, the model parameters can comprise information related to layer thicknesses, layer permittivities, layer permeabilities and / or number of layers within the target area.

[0119] The method can comprise initializing the model parameters. This process can comprise providing a respective value to each of the model parameters. Typically, at least some of the model parameters may be unknown. This can be particularly the case with layer thicknesses and / or layer permittivities. Nevertheless, it can be advantageous to initialize even the unknown parameters.

[0120] The initialization of the unknown model parameters can be based on at least one bound associated with a respective one of the unknown model parameters. Said at least one bound can be a lower and / or upper bound.

[0121] The initialization of the unknown model parameters can be based on at least one initial estimate of said unknown model parameters.

[0122] Initializing the unknown model parameters based on at least one bound and / or based on at least one initial estimate can be advantageous as it can facilitate determining the model parameters more accurately and faster.

[0123] The method can comprise optimizing the model parameters such that the output of the computer model fits with the measured data set. That is, the computer model of the target area can yield a different output for the same input if the model parameters are changed. The method can thus attempt to determine the optimal model parameters which can yield an output that is most similar (and ideally the same) as the measured data set. In other words, the method can attempt to determine the optimal model parameters such that the computer model can more similarly replicate the effects of the target area on measurement signals.

[0124] Determining the at least one layer-parameter based on the computer model comprises determining the at least one layer-parameter based on the optimized model parameters.

[0125] Optimizing the model parameters can comprise comparing the measured data set to the output of the computer model using different model parameters and iteratively adjusting the model parameters to minimize the difference between the measured data set and the output of the computer model.

[0126] Determining the optimal model parameters can comprises executing an optimization algorithm configured to solve a non-convex problem. This can increase the likelihood of determining the globally optimum model parameters.

[0127] Determining the optimal model parameters can comprise executing an optimization algorithm configured to solve a non-linear least squares problem.

[0128] Determining the optimal model parameters can comprises executing a second-order optimization method, such as, the Levenberg-Marquardt algorithm. Determining at least one layer-parameter of the target area can comprise providing at least one initial value for at least one of the at least one layer-parameter. Said at least one initial value can for example be used for initializing the model parameters.

[0129] Providing at least one initial value for at least one of the at least one layer-parameter can comprise providing an expected value for at least one of the at least one layer- para meter.

[0130] Providing at least one initial value for at least one of the at least one layer-parameter can comprise providing an upper and / or a lower bound for at least one of the at least one layer-parameter.

[0131] Providing at least one initial value for at least one of the at least one layer-parameter can comprise providing a number of layers can comprise by the target area.

[0132] In some embodiments, determining at least one layer-parameter of the target area can comprise utilizing at least one known layer-parameter. That is, information about one or more layers can be known in advance. Said information can therefore be utilized. This can lower the complexity of determining the layer parameters, therefore leading to a faster determination.

[0133] In some embodiments the at least one known-layer parameter can comprise a number of layers of the target area. Said parameter can typically be known from the manufacturing process.

[0134] In some embodiments the at least one known-layer parameter can correspond to at least one known layer of the target area. For example, if the material of a layer can be known in advance, then known properties of said material can be used to at least estimate at least one layer parameter of said layer.

[0135] The method can comprise determining the at least one layer-parameter for at least one other layer of the target area different from the known layer to which the at least one known-layer parameter corresponds.

[0136] In some embodiments the incidence angle can be indicative of an angle between a direction of the measurement path and a normal vector of the target area.

[0137] A direction of the measurement path can coincide with a direction of motion of the respective measurement signal. That is, each measurement signal is emitted along a respective measurement path such that the direction of propagation of the measurement signal coincides with the measurement path. In other words, the direction of propagation and the measurement path can be used interchangeably. The incidence angle of a measurement path can be an angle between the respective measurement path and a line perpendicular to the target area. That is, each measurement path can be characterized by a respective incidence angle, which can be an angle between the measurement path of the respective measurement signal and a line perpendicular to the target area.

[0138] In some embodiments the measured data set can comprise data obtained from each measurement associated with the respective incidence angle of the respective measurement path. In other words, for each measurement the incidence angle can be known and the data obtained from each measurement can be associated with the respective incidence angle.

[0139] In some embodiments the measured data set can comprise data obtained from each measurement associated with a respective frequency of a respective measurement signal used to perform the respective measurement. In other words, for each measurement the frequency of the measurement signal used for the measurement can be known and the data obtained from each measurement can be associated with the respective frequency.

[0140] In some embodiments the measured data set can comprise data obtained from each measurement associated with a respective polarization of a respective measurement signal used to perform the respective measurement. In other words, for each measurement the polarization of the measurement signal used for the measurement can be known and the data obtained from each measurement can be associated with the respective polarization.

[0141] In some embodiments the measured data set can comprise data obtained from each measurement associated with an indication of a side of the target area wherein a measurement signal used to perform the respective measurement can be incident on.

[0142] In some embodiments performing a measurement can comprise measuring an amplitude and a phase of the received portion of each measurement signal.

[0143] In some embodiments the received portion of each measurement signal can comprise a transmitted part of the measurement signal. The transmitted part can comprise a part of the measurement signal that can be transmitted through the target area. The transmitted part can thus follow a propagation path from the transmitter, through the target area and to the receiver.

[0144] In some embodiments the reflected part can comprise a part of the measurement signal that can be reflected at least once by an outer surface of the target area. The reflected part can thus be reflected at least once by an outer surface of the target area before being received by the receiver. In some embodiments performing a measurement can comprise determining a transmission property of the target area. That is, performing a measurement can comprise performing a transmission measurement. A transmission measurement of the target area can comprise assessing the extent to which the target area can affect the transmission of electromagnetic waves passing through the target area. Typically, a transmission measurement can be performed by placing the target area between a transmitter and a receiver. The transmitter can emit the measurement signal which can then be transmitted through the target area. The target area can be configured to be transparent to the specific frequency or range of frequencies of the measurement signal. However, no material can be perfectly transparent, and the target can cause attenuation (reduction in signal strength) and / or phase shift to the measurement signal. The receiver on the other side of the target area can measure the signals after they have passed through the radome. This measurement can include assessing the signal strength (i.e., amplitude) and / or phase. Additionally, any other changes in the signal characteristics can be assessed. The results of the measurement can be analysed to determine the effect of the target area on the measurement signal transmitted through the target area. This analysis can comprise quantifying the effect of the target area in terms of signal loss or distortion.

[0145] In some embodiments performing a measurement can comprise determining a reflection property of the target area. That is, performing a measurement can comprise performing a reflection measurement. A reflection measurement of the target area can comprise assessing the extent to which the target area can reflect electromagnetic waves. The reflection measurement can comprise a receiver receiving a part of the measurement signal that is reflected by an outer surface of the target area. This measurement can include assessing the strength of the reflected part and / or its phase. In addition, it may comprise assessing any changes in the characteristics of the reflected part due to the interaction with the target area.

[0146] Preferably, performing a measurement can comprise determining a transmission coefficient and / or a reflection coefficient of the target area. In particular, determining at least transmission coefficient may be preferable.

[0147] In some embodiments the measuring device can be configured such that, for each antenna pair, the respective transmitter and the respective receiver face each other. This way a straight transmission path may exist between the transmitter and the receiver.

[0148] In some embodiments the measuring device can be configured such that, for each antenna pair, the respective transmitter and the respective receiver can be provided at a fixed distance from each other. This can facilitate maintaining a fixed transmission path length between the transmitter and the receiver during each of the measurements.

[0149] In some embodiments the measuring device can be configured such that, for each antenna pair, the respective transmitter can be configured to emit electromagnetic waves with a frequency of at least 20 GHz and at most 160 GHz, such as, at least 70 GHz and at most 90 GHz. This can be particularly advantageous for measuring radomes (i.e., radar covers) used in the automotive industry.

[0150] In some embodiments the measuring device can be configured such that, for each antenna pair, the respective receiver can be configured to receive electromagnetic waves with a frequency of at least 20 GHz and at most 160 GHz, such as, at least 70 GHz and at most 90 GHz. This can be particularly advantageous for measuring radomes (i.e., radar covers) used in the automotive industry.

[0151] In some embodiments the measurement signal can be an electromagnetic wave with a frequency of at least 20 GHz and at most 160 GHz, such as, at least 70 GHz and at most 90 GHz. This can be particularly advantageous for measuring radomes (i.e., radar covers) used in the automotive industry.

[0152] In some embodiments the measuring device can be configured such that, for each antenna pair, the respective measurement path extends from the transmitter to the receiver. Generally, for each antenna pair, the measurement path can coincide with a transmission path between the transmitter and the receiver.

[0153] In some embodiments the measurement path can be an imaginary line between the respective transmitter and the respective receiver. That is, the measurement path is not a physical component of the present invention.

[0154] In some embodiments the measurement path can be coincident with a line of sight between the respective transmitter and the respective receiver. It will be understood, that said line of sight may be present when no target area or device under test is positioned between the transmitter and the receiver.

[0155] In some embodiments the measurement path can be coincident with a boresight of the respective transmitter.

[0156] In some embodiments the measurement path can be coincident with a boresight of the respective receiver. In some embodiments for each antenna pair, the respective transmitter and the respective receiver can be aligned such that the measurement path, the antenna boresight of the respective transmitter and the antenna boresight of the respective receiver can be coincident. This can maximize signal strength, reduce interference, and ensure accurate signal reception or transmission between the transmitter and the receiver.

[0157] In some embodiments, the data processing system may be external to the measuring device.

[0158] Alternatively, the data processing system and the measuring device may be integrated into a single device. For example, the measuring device may comprise the processing system.

[0159] The data processing system can also be referred to as a processing system for the sake of brevity. The processing system can comprise one or more processing units configured to carry out computer instructions of a program (i.e., machine readable and executable instructions). The processing unit(s) can be singular or plural. For example, the processing system may comprise at least one of CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), APU (Accelerated Processing Unit) and / or FPGA (Field-Programmable Gate Array).

[0160] The processing system can comprise memory components, such as main memory (e.g., random-access memory), cache memory and / or secondary memory (e.g., HDD, SDD). The processing system may comprise volatile and / or non-volatile memory such an SDRAM (Synchronous Dynamic Random-Access Memory), DRAM (Dynamic Random-Access Memory)

[0161] SRAM (Static Random-Access Memory), flash memory, MRAM (Magneto-resistive Random- Access Memory), F-RAM (Ferroelectric Random-Access Memory) and / or P-RAM (Phase- Change Random-Access Memory).

[0162] The processing system can comprise internal communication interfaces (e.g., busses) configured to facilitate electronic data exchange between components of the data processing system, such as the communication between the memory components and the processing components. The data processing system can comprise external communication interfaces configured to facilitate electronic data exchange with devices external to the data processing system.

[0163] The data processing system can be configured for wired and / or wireless data communication. For example, the processing system can be configured to transfer electronic data using a standardized communication protocol. For example, the data processing system can comprise a network card and / or a USB port. The processing system can comprise a system-on-chip comprising processing units, memory components and busses.

[0164] The processing system may be a centralized or distributed computing system.

[0165] In some embodiments the measuring device can comprise a clamp structure wherein the clamp structure can comprise a first mount configured for mounting at least one transmitter; a second mount configured for mounting at least one transmitter; a base frame and wherein the first mount and the second mount extend from the same side of the base frame.

[0166] The clamp structure can provide a stable structure for the transmitter and receiver to be mounted. As discussed, it can be advantageous to have the transmitter and the receiver aligned with each-other such that most of the radiated electromagnetic waves emitted by the transmitter can be received by the receiver. The shape of the clamp structure can facilitate this alignment. Further, it can be advantageous that the distance between the two antennas be kept constant. The clamp structure, more particularly the base frame, can facilitate keeping the distance between the transmitter and receiver constant.

[0167] The clamp structure can further facilitate the moving the measuring device, without changing the relative position between the transmitter and the receiver. This can particularly facilitate changing the incidence angle for the measurements.

[0168] In some embodiments the measuring device can be configured such that the first mount, the second mount, and the base frame form a substantially U-shaped structure of the clamp structure.

[0169] In some embodiments the first mount and the second mount can be identical.

[0170] In some embodiments the target area can be a portion of the device under test around the intersection between the measurement path and the device under test.

[0171] In some embodiments the device under test can be a radome configured to cover at least in part a radar. In other words, the present invention can be used to measure radomes. Measuring radomes may allow evaluating their effectiveness in maintaining signal quality. It can quantify signal characteristics, ensuring compliance with design specifications. Measuring radomes can aids in identifying manufacturing defects, contributing to product consistency. It can further facilitate assessing and / or quantifying how radomes can impact radar signal quality. Further still, radome measurements can assist in choosing suitable radome materials by evaluating their effect to electromagnetic waves. In a second aspect, the present invention relates to a system for measuring a target area of a device under test, the system comprising a measuring device configured to perform a measurement by emitting a measurement signal along a measurement path and receiving a received portion of the measurement signal; the measuring device configured to perform a plurality of measurements for a plurality of measurement paths, respectively, to thereby obtain a measured data set; wherein for at least some of the measurements the respective measurement paths intersect the target area at different incidence angles.

[0172] The system may further comprise a data processing system configured to determine at least one layer-parameter of the target area based on the measured data set.

[0173] The system may further comprise a data positioning system configured to generate a relative motion between the measuring device and the target area to define at least some of the measurement paths that intersect the target area at different incidence angles.

[0174] The system may be configured to carry out the method as discussed above and below.

[0175] The present invention further relates to the following numbered embodiments.

[0176] Below, method embodiments will be discussed. These embodiments are abbreviated by the letter "M" followed by a number. When reference is herein made to method embodiments, these embodiments are meant.

[0177] Ml. A method for measuring a target area (35) of a device under test (30), comprising providing a measuring device (10) configured to perform a measurement by emitting a measurement signal along a measurement path (15) and receiving a received portion of the measurement signal; with the measuring device (10), performing a plurality of measurements for a plurality of measurement paths (15), respectively, to thereby obtain a measured data set; wherein for at least some of the measurements the respective measurement paths (15) intersect the target area (35) at different incidence angle.

[0178] M2. The method according to the preceding embodiment, wherein the method comprises performing at least some of the plurality of measurements with a time-delay between each-other.

[0179] M3. The method according to any of the preceding embodiments, wherein the method comprises performing at least some of the plurality of measurements simultaneously or quasi-simultaneously. M4. The method according to any of the preceding embodiments, wherein the measuring device (10) comprises at least one antenna pair (12, 14), wherein each antenna pair (12, 14) comprises a transmitter (12) and a receiver (14) and wherein each antenna pair (12, 14) defines a respective measurement path (15).

[0180] M5. The method according to the preceding embodiment, wherein the measuring device (10) is configured such that a single antenna pair (12, 14) is utilized to perform the plurality of measurements.

[0181] M6. The method according to any of the preceding embodiments, wherein the measuring device (10) is configured such that at any instant of time a single measurement path (15) is defined.

[0182] M7. The method according to any of the preceding embodiments, wherein the method comprises generating a relative motion between the measuring device (10) and the target area (35) to define at least some of the measurement paths (15) that intersect the target area (35) at different incidence angles.

[0183] M8. The method according to the preceding embodiment, wherein the method comprises performing at least some of the plurality of measurements during the relative motion.

[0184] M9. The method according to any of the 2 preceding embodiments, wherein the relative motion comprises a rotational motion of the measuring device (10) and / or of the target area (35).

[0185] M10. The method according to any of the preceding embodiments and with the features of embodiment M4, wherein the measuring device (10) comprises a plurality of antenna pairs (12, 14) respectively defining at least some of the measurement paths (15) that intersect the target area (35) at different incidence angles.

[0186] Mil. The method according to the preceding embodiment, wherein the method comprises performing at least some of the plurality of measurements with different antenna pairs (12, 14).

[0187] M12. The method according to any of the 2 preceding embodiments, wherein the method comprises performing at least some of the plurality of measurements by utilizing at least two of the antenna pairs (12, 14) simultaneously or quasi-simultaneously. M13. The method according to any of the 3 preceding embodiments, wherein the method comprises performing at least some of the plurality of measurements by utilizing at least two of the antenna pairs (12, 14) at different frequencies.

[0188] M14. The method according to any of the 4 preceding embodiments, wherein the method comprises performing at least some of the plurality of measurements by utilizing at least two of the antenna pairs (12, 14) at different time intervals.

[0189] M15. The method according to any of the preceding embodiments, wherein the measuring device (10) is configured such that at an instant of time multiple measurement paths (15) intersecting the target area (35) at different incidence angles are defined.

[0190] M16. The method according to any of the preceding embodiments, wherein the target area comprises multiple layers stacked on top of each other.

[0191] M17. The method according to any of the preceding embodiments, comprising with a data processing system, determining at least one layer-parameter of the target area (35) based on the measured data set.

[0192] M18. The method according to the preceding embodiment, wherein each layer-parameter is indicative of a layer-property of the target area (35).

[0193] M19. The method according to any of the 2 preceding embodiments, wherein one layerparameter is indicative of a number of layers of the target area (35).

[0194] M20. The method according to any of the 3 preceding embodiments, wherein one layerparameter is indicative of a respective layer thickness of at least one layer of the target area (35).

[0195] M21. The method according to any of the 4 preceding embodiments, wherein one layerparameter is indicative of a respective layer electromagnetic property of at least one layer of the target area (35).

[0196] M22. The method according to the preceding embodiment, wherein the respective layer electromagnetic property of a layer is indicative of a permeability of said layer. M23. The method according to any of the 2 preceding embodiments, wherein the respective layer electromagnetic property of a layer is indicative of a permittivity of said layer.

[0197] M24. The method according to any of the preceding embodiments and with the features of embodiment M17, wherein determining at least one layer-parameter of the target area (35) comprises determining a plurality of layer-parameters of the target area (35) simultaneously.

[0198] M25. The method according to the preceding embodiment, wherein at least some of the layer-parameters of the target area (35) correspond to different layers of the target area (35).

[0199] M26. The method according to any of the 2 preceding embodiments, wherein the method comprises determining the plurality of layer-parameters of the target area (35) simultaneously by simultaneously optimizing the plurality of layer-parameters.

[0200] M27. The method according to any of the 3 preceding embodiments, wherein the plurality of layer-parameters of the target area (35) is indicative of a layer thickness and of a layer electromagnetic property of each one of at least some of the layers of the target area (35).

[0201] M28. The method according to any of the 4 preceding embodiments, wherein the plurality of layer-parameters of the target area (35) is indicative of a layer thickness, of a layer permeability and of a layer permittivity of each one of at least some of the layers of the target area (35).

[0202] M29. The method according to any of the preceding embodiments, comprising with a data processing system, determining at least one target area parameter, wherein each target area parameter is indicative of an end-to-end property of the target area (35).

[0203] M30. The method according to the preceding embodiment, wherein the method comprises determining the at least one target area parameter based on the measured data set.

[0204] M31. The method according to any of the 2 preceding embodiments and with the features of embodiment M17, wherein the method comprises determining the at least one target area parameter based on the at least one layer-parameter. M32. The method according to any of the 3 preceding embodiments, wherein one target area parameter is indicative of an end-to-end thickness of the target area (35).

[0205] M33. The method according to any of the 4 preceding embodiments, wherein one target area parameter is indicative of an end-to-end electromagnetic property of the target area (35).

[0206] M34. The method according to the preceding embodiment, wherein the end-to-end electromagnetic property of the target area (35) is indicative of an end-to-end permeability of the target area (35).

[0207] M35. The method according to any of the 2 preceding embodiments, wherein the end- to-end electromagnetic property of the target area (35) is indicative of an end-to-end permittivity of the target area (35).

[0208] M36. The method according to any of the preceding embodiments and with the features of embodiment M17, wherein the method comprises obtaining, using a data processing device and from a memory, a computer model of the target area; wherein said computer model comprises model parameters indicative of layer properties of the target area; wherein the computer model is configured to digitally replicate a measurement by receiving as input data indicative of a measurement signal incident on the target area and calculate an output indicative of an expected received portion of the measurement signal; wherein the method comprises determining the at least one layer-parameter based on the computer model.

[0209] M37. The method according to the preceding embodiment, wherein the computer model is an analytical model based on electromagnetic wave propagation principles and Maxwell's equations.

[0210] M38. The method according to any of the 2 preceding embodiments, wherein the output of the computer model is indicative of an expected measured data set.

[0211] M39. The method according to any of the 3 preceding embodiments, wherein the input to the computer model is configured to characterize, at least in part, the measurement signal incident on the target area. M40. The method according to any of the 4 preceding embodiments, wherein the input to the computer model is configured to fully characterize the measurement signal incident on the target area.

[0212] M41. The method according to any of the 5 preceding embodiments, wherein the input to the computer model comprises a frequency, an amplitude, a polarization and / or an incidence angle of the measurement signal.

[0213] M42. The method according to any of the 6 preceding embodiments, wherein the model parameters comprise information related to layer properties of the target area.

[0214] M43. The method according to any of the 7 preceding embodiments, wherein the model parameters comprise information related to layer thicknesses, layer permittivities, layer permeabilities and / or number of layers within the target area.

[0215] M44. The method according to any of the 9 preceding embodiments, wherein the method comprises initializing the model parameters.

[0216] M45. The method according to any of the 10 preceding embodiments, wherein at least some of the model parameters are unknown and the method comprises initializing the unknown model parameters.

[0217] M46. The method according to the preceding embodiment, wherein initializing the unknown model parameters comprises using at least one bound associated with a respective one of the unknown model parameters.

[0218] M47. The method according to any of the 2 preceding embodiments, wherein initializing the unknown model parameters comprises using at least one initial estimate associated with a respective one of the unknown model parameters.

[0219] M48. The method according to any of the 13 preceding embodiments, comprises optimizing the model parameters such that the output of the computer model fits with the measured data set.

[0220] M49. The method according to the preceding embodiment, wherein determining the at least one layer-parameter based on the computer model comprises determining the at least one layer-parameter based on the optimized model parameters. M50. The method according to any of the 2 preceding embodiments, wherein optimizing the model parameters comprises comparing the measured data set to the output of the computer model using different model parameters; iteratively adjusting the model parameters to minimize the difference between the measured data set and the output of the computer model.

[0221] M51. The method according to any of the 3 preceding embodiments, wherein determining the optimal model parameters comprises executing an optimization algorithm configured to solve a non-convex problem.

[0222] M52. The method according to any of the 4 preceding embodiments, wherein determining the optimal model parameters comprises executing an optimization algorithm configured to solve a non-linear least squares problem.

[0223] M53. The method according to any of the 5 preceding embodiments, wherein determining the optimal model parameters comprises executing a second-order optimization method, such as, the Levenberg-Marquardt algorithm

[0224] M54. The method according to any of the preceding embodiments and with the features of embodiment M17, wherein determining at least one layer-parameter of the target area (35) comprises providing at least one initial value for at least one of the at least one layerparameter.

[0225] M55. The method according to the preceding embodiment, wherein providing at least one initial value for at least one of the at least one layer-parameter comprises providing an expected value for at least one of the at least one layer-parameter.

[0226] M56. The method according to any of the 2 preceding embodiments, wherein providing at least one initial value for at least one of the at least one layer-parameter comprises providing an upper and / or a lower bound for at least one of the at least one layerparameter.

[0227] M57. The method according to any of the 3 preceding embodiments, wherein providing at least one initial value for at least one of the at least one layer-parameter comprises providing a number of layers comprised by the target area (35). M58. The method according to any of the preceding embodiments and with the features of embodiments M16 and M17, wherein determining at least one layer-parameter of the target area (35) comprises utilizing at least one known layer-parameter.

[0228] M59. The method according to the preceding embodiment, wherein the at least one known-layer parameter comprises a number of layers of the target area (35).

[0229] M60. The method according to any of the 2 preceding embodiments, wherein the at least one known-layer parameter corresponds to at least one known layer of the target area (35).

[0230] M61. The method according to the preceding embodiment, wherein the method comprises determining the at least one layer-parameter for at least one other layer of the target area (35) different from the known layer to which the at least one known-layer parameter corresponds.

[0231] M62. The method according to any of the preceding embodiments, wherein the incidence angle is indicative of an angle between a direction of the measurement path (15) and a normal vector of the target area (35).

[0232] M63. The method according to any of the preceding embodiments, wherein a direction of the measurement path (15) coincides with a direction of motion of the respective measurement signal.

[0233] M64. The method according to any of the preceding embodiments, wherein each of the incidence angles (15) is an angle between the respective measurement path (15) and a line perpendicular to the target area (35).

[0234] M65. The method according to any of the preceding embodiments, wherein the measured data set comprises data obtained from each measurement associated with the respective incidence angle of the respective measurement path (15).

[0235] M66. The method according to any of the preceding embodiments, wherein the method comprises data obtained from each measurement associated with a respective frequency of a respective measurement signal used to perform the respective measurement. M67. The method according to any of the preceding embodiments, wherein the measured data set comprises data obtained from each measurement associated with a respective polarization of a respective measurement signal used to perform the respective measurement.

[0236] M68. The method according to any of the preceding embodiments, wherein the measured data set comprises data obtained from each measurement associated with an indication of a side of the target area (35) wherein a measurement signal used to perform the respective measurement is incident on.

[0237] M69. The method according to any of the preceding embodiments, wherein performing a measurement comprises measuring an amplitude and a phase of the received portion of each measurement signal.

[0238] M70. The method according to any of the preceding embodiments, wherein the received portion of each measurement signal comprises a transmitted part of the measurement signal.

[0239] M71. The method according to the preceding embodiment, wherein the transmitted part comprises a part of the measurement signal that is transmitted through the target area (35).

[0240] M72. The method according to any of the preceding embodiments, wherein the received portion of each measurement signal comprises a reflected part of the measurement signal.

[0241] M73. The method according to the preceding embodiment, wherein the reflected part comprises a part of the measurement signal that is reflected at least once by an outer surface of the target area (35).

[0242] M74. The method according to any of the preceding embodiments, wherein performing a measurement comprises determining a transmission property of the target area (35).

[0243] M75. The method according to any of the preceding embodiments, wherein performing a measurement comprises determining a reflection property of the target area (35).

[0244] M76. The method according to any of the preceding embodiments, wherein performing a measurement comprises determining a transmission coefficient and / or a reflection coefficient of the target area (35). M77. The method according to any of the preceding embodiments and with the features of embodiment M4, wherein the measuring device (10) is configured such that, for each antenna pair (12, 14), the respective transmitter (12) and the respective receiver (14) face each-other.

[0245] M78. The method according to any of the preceding embodiments, wherein the measuring device (10) is configured such that, for each antenna pair (12, 14), the respective transmitter (12) and the respective receiver (14) are provided at a fixed distance from each-other.

[0246] M79. The method according to any of the preceding embodiments, wherein the measuring device (10) is configured such that, for each antenna pair (12, 14), the respective transmitter (12) is configured to emit electromagnetic waves with a frequency of at least 20 GHz and at most 160 GHz, such as, at least 70 GHz and at most 90 GHz.

[0247] M80. The method according to any of the preceding embodiments, wherein the measuring device (10) is configured such that, for each antenna pair (12, 14), the respective receiver (14) is configured to receive electromagnetic waves with a frequency of at least 20 GHz and at most 160 GHz, such as, at least 70 GHz and at most 90 GHz.

[0248] M81. The method according to any of the preceding embodiments, wherein the measurement signal is an electromagnetic wave with a frequency of at least 20 GHz and at most 160 GHz, such as, at least 70 GHz and at most 90 GHz.

[0249] M82. The method according to any of the preceding embodiments, wherein the measuring device (10) is configured such that, for each antenna pair (12, 14), the respective measurement path (15) extends from the transmitter (12) to the receiver (14).

[0250] M83. The method according to any of the preceding embodiments, wherein the measurement path (15) is an imaginary line between the respective transmitter (12) and the respective receiver (14).

[0251] M84. The method according to any of the preceding embodiments, wherein the measurement path (15) is coincident with a line of sight between the respective transmitter (12) and the respective receiver (14). M85. The method according to any of the preceding embodiments, wherein the measurement path (15) is coincident with a boresight of the respective transmitter (12).

[0252] M86. The method according to any of the preceding embodiments, wherein the measurement path (15) is coincident with a boresight of the respective receiver (14).

[0253] M87. The method according to any of the preceding embodiments, wherein for each antenna pair (12, 14), the respective transmitter (12) and the respective receiver (14) are aligned such that the measurement path (15), the antenna boresight of the respective transmitter (12) and the antenna boresight of the respective receiver (14) are coincident.

[0254] M88. The method according to any of the preceding embodiments and with the features of embodiment M17, wherein the measuring device (10) further comprises the data processing system (20).

[0255] M89. The method according to any of the preceding embodiments, wherein the measuring device (10) comprises a clamp structure (60) wherein the clamp structure (60) comprises a first mount (62) configured for mounting at least one transmitter (12); a second mount (64) configured for mounting at least one transmitter (14); a base frame (66) and wherein the first mount (62) and the second mount (64) extend from the same side of the base frame (66).

[0256] M90. The method according to the preceding embodiment, wherein the measuring device (10) is configured such that the first mount (62), the second mount (64) and the base frame (66) form a substantially U-shaped structure of the clamp structure (60).

[0257] M91. The method according to any of the 2 preceding embodiments, wherein the first mount (62) and the second mount (66) are identical.

[0258] M92. The method according to any of the preceding embodiments, wherein the target area (35) is a portion of the device under test (30) around the intersection between the measurement path (15) and the device under test (30).

[0259] M93. The method according to any of the preceding embodiments, wherein the device under test (30) is a radome configured to cover at least in part a radar. Below, system embodiments will be discussed. These embodiments are abbreviated by the letter "S" followed by a number. When reference is herein made to system embodiments, these embodiments are meant.

[0260] 51. A system for measuring a target area (35) of a device under test (30), comprising a measuring device (10) configured to perform a measurement by emitting a measurement signal along a measurement path (15) and receiving a received portion of the measurement signal; the measuring device (10) configured to perform a plurality of measurements for a plurality of measurement paths (15), respectively, to thereby obtain a measured data set; wherein for at least some of the measurements the respective measurement paths (15) intersect the target area (35) at different incidence angle.

[0261] 52. The system according to the preceding embodiment, further comprising a data processing system (20) configured to determine at least one layer-parameter of the target area (35) based on the measured data set.

[0262] 53. The system according to any of the 2 preceding embodiments, further comprising a data positioning system (40) configured to generate a relative motion between the measuring device (10) and the target area (35) to define at least some of the measurement paths (15) that intersect the target area (35) at different incidence angles.

[0263] 54. The system according to any of the 3 preceding embodiments, configured to carry out the method according to any of the preceding method embodiments.

[0264] Brief description of the drawings

[0265] Fig. 1 illustrates a measuring system;

[0266] Fig. 2 illustrate different measurement paths with difference incidence angles;

[0267] Fig. 3 illustrates a measuring device with multiple antenna pairs;

[0268] Fig. 4 illustrates different parts of a received portion during a measurement;

[0269] Fig. 5 depicts a flowchart of a method for measuring a target area of a device under test;

[0270] Fig. 6 illustrates a measuring device comprising a clamp structure. Detailed description of the drawings

[0271] In the following, exemplary embodiments of the invention will be described, referring to the figures. These examples are provided to facilitate further understanding of the invention, without limiting its scope. Moreover, in the following description, a series of features and / or steps are described. The skilled person will appreciate that unless required by the context, the order of features and steps is not critical for the resulting configuration and its effect. Further, it will be apparent to the skilled person that irrespective of the order of features and steps, the presence or absence of time delay between steps, can be present between some or all of the described steps.

[0272] Throughout the description of the drawings, like features are denoted by like reference numerals. However, for ease of illustration and brevity of the description, some reference numerals may be omitted in some of the Figures.

[0273] Throughout the description, the terms wave, electromagnetic wave, signal and electromagnetic signal are used interchangeably to refer to electromagnetic waves. Moreover, the terms emit, transmit and radiate are also used interchangeably.

[0274] Fig. 1 illustrates a measuring system. The measuring system can comprise a measuring device 10, a data processing system 20 and a positioning system 40. It will be understood that the positioning system 40 and the data processing system 20 can be optional. In particular, the positioning system 40 can be optional. Moreover, throughout the description the data processing system 20 may also be referred to as processing system 20, for the sake of brevity.

[0275] The measuring device 10 can comprise at least one antenna pair 12, 14, each comprising a respective transmitter 12 and a respective receiver 14. The transmitter 12 and the receiver 14 can face each-other. The transmitter 12 and the receiver 14 can be provided at a fixed distance from each-other. In some embodiments, the processing system 20 can be part of the measuring device 10. That is, the processing system 20 and the measuring device 10 can form a single device. Hereinafter, whenever referring the measuring device 10, unless otherwise specified, both embodiments are meant - i.e., the measuring device 10 comprising the processing system 20 and the measuring device 10 and the processing system 20 being separate from each other. A device under test 30 (i.e., DUT) can be provided between the transmitter 12 and the receiver 14. It will be understood that the DUT may not be a part of the measuring system, but rather an external part that can be measured by the measuring system. The transmitter 12 can be configured to emit electromagnetic waves. Preferably, the transmitter 12 can be configured to emit electromagnetic waves with a frequency between 20 GHz to 160 GHz, such as, between 70 GHz and 90 GHz. The transmitter 12 can comprise at least one transmitting antenna 12.

[0276] The receiver 14 can be configured to receive electromagnetic waves. Preferably, the receiver 1 can be configured to receive electromagnetic waves with a frequency between 20 GHz to 160 GHz, such as, between 70 GHz and 90 GHz. The receiver 14 can comprise at least one receiving antenna 14.

[0277] In some embodiments, the transmitter 12 and / or receiver 14 can be configured as transceivers, i.e., can be configured to emit and receive electromagnetic waves.

[0278] The measuring device 10 can define a measurement path 15 between the transmitter 12 and receiver 14. In particular, each antenna pair 12, 14 can define a respective measurement path 15. It will be understood that the measurement path 15 can refer to an imaginary line between the transmitter 12 and receiver 14. The measurement path 15 can be coincident with a line of sight between the transmitter 12 and receiver 14. The measurement path 15 can be coincident with a boresight of the transmitter 12. The latter can refer to an axis along which the transmitter 15 can emit the maximum power, i.e., the axis of maximum gain. Alternatively or additionally, the measurement path 15 can be coincident with a boresight of the receiver 14. The latter can refer to an axis along which the receiver 14 can sense (or receive) the maximum power, i.e., the axis of maximum gain. For most antennas the boresight can typically be the axis of symmetry of the antenna. Therefore, in some embodiments, the measurement path 15 can be coincident with an axis of symmetry of the transmitter 12 and / or with an axis of symmetry of the receiver 14.

[0279] For each antenna pair 12, 14, the transmitter 12 and the receiver 14 can be aligned such that the respective measurement path 15 can be an antenna boresight and / or an axis of symmetry of the respective transmitter 12 and of the respective receiver 14.

[0280] The DUT can be provided between the transmitter 12 and receiver 14, such that it can intersect the antenna axis 13 and such that a first side 32 can face the transmitter 12 and a second side 34 can face the receiver 14. The first side 32 and the second side 34 can be opposite sides of the DUT. That is, the first side 32 can refer to the side of the DUT that can face the transmitter 12 and the second side 34 can refer to the side of the DUT that can face the receiver 14. A portion of the DUT around the intersection between the measurement path 15 and the DUT can be referred to as the target area 35, which is illustrated in Fig. 1 as a filled box. The target area 35 can refer to an area of the DUT which can intersect signals generated by the transmitter 12.

[0281] The DUT can for example be a radome. That is, the device under test 30 can be a radome configured to cover at least in part a radar. It will be understood, that the first side 32 of the DUT (i.e., the side of the DUT facing the transmitter 12) can be any side of the radome. For example, the first side 32 can be a transmission side of the radome 30. Similarly, the second side 34 of the DUT (i.e., the side of the DUT facing the receiver 14) can be any side of the radome. For example, the second side 34 can be the reception side of the radome 30. Generally, any two opposite sides of the radome 30 can form the first side 32 and the second side 34, when the radome 30 is the DUT. The allocation of sides of a radome 30 as the first side 32 and the second side 34 can be determined based on the orientation of the radome 30 when positioned between the transmitter 12 and the receiver 14.

[0282] As illustrated in Fig. 1, the target area 35 can be provided closer to the receiver 14 than to the transmitter 12. This can be particularly advantageous for determining a reflection property of the second side 34. The closer the target area 35 can be to the receiver 14 the higher the likelihood that there can be signals reflected by the second side 34 and received by the receiver 14, e.g., the higher the likelihood that there will be signals following the second reflection path P2 illustrated in Fig. 4a. Moreover, the closer the target area 35 can be to the receiver 14, the longer the first reflection path Pl can be and the shorter the second reflection path P2 can be. Thus, reflections following the second reflection path P2 can be dominant, while reflections following the first reflection path Pl can be negligible. The same is true, mutatis mutandis, for the second order reflection paths Pl' and P2' illustrated in Fig. 4b.

[0283] Alternatively, the target area 35 can be provided closer to the transmitter 12 than to the receiver 14 (not shown). This can be particularly advantageous for determining a reflection property of the first side 32. The closer the target area 35 can be to the transmitter 12 the higher the likelihood that reflections created by the first side 32 can be reflected back towards the receiver 14, e.g., the higher the likelihood that there will be signals following the first reflection path Pl illustrated in Fig. 4a. Moreover, the closer the target area 35 can be to the transmitter 12, the shorter the first reflection path Pl can be and the longer the second reflection path P2 can be. Thus, reflections following the first reflection path Pl can be dominant, while reflections following the second reflection path P2 can be negligible. The same is true, mutatis mutandis, for the second order reflection paths Pl' and P2' illustrated in Fig. 4b. In this regard, providing the target area 35 closer to the transmitter 12 or closer to the receiver 14 can lead to more robustness against incidence angle different than 90°. In other words, even if the target area 35 may not be positioned completely perpendicularly with the measurement path 15, the likelihood that reflections created by the target area 35 can be reflected away from the measuring device 10 and not be received by the receiver 14 can be reduced by providing the target area 35 closer to the receiver 14 or closer to the transmitter 12.

[0284] The measuring device 10 can optionally comprise reflecting surfaces 17T, 17R which can be configured to increase the likelihood that signals reflected by target area 35 can be reflected back towards the receiver 14.

[0285] The measuring device can comprise reflecting surface 17T which can be configured to increase the likelihood that signals reflected by the first surface 32 can be reflected back towards the receiver 14. Surfaces of the transmitter 12 can also reflect towards the receiver 14 signals that were initially reflected by the first side 32. However, the transmitter 12 may comprise a small surface area. Therefore, signals which were initially reflected by the first side 32 of the target area 35 may "miss" the transmitter 12 and may therefore travel away and not be directed towards the receiver 14. Reflecting surface 17T can alleviate this by providing additional surface for "capturing" and directing signals towards the receiver 14. Said reflecting surface 17T can preferably be provided near the transmitter 12, as illustrated in Fig. 2. The reflecting surface 17T can be a surface of a component wherein the transmitter 12 is mounted or connected to. For example, the reflecting surface 17T can be a surface of an up-converter that can typically be positioned behind the transmitter 12. Said reflecting surface 17T can also be referred to as a first reflecting surface 17T.

[0286] The measuring device can comprise reflecting surface 17R which can be configured to increase the likelihood that signals reflected by the second surface 34 can be reflected back towards the receiver 14. That is a second reflecting surface 17R can be provided near the receiver 14. It can be advantageous as it can increase the likelihood that signals reflected by the second surface 34 can be reflected back towards the second surface 34, wherein they can be reflected again towards the receiver 14. For example, the second reflecting surface 17R can be a surface of a down-converter that can typically be positioned behind the receiver 14.

[0287] The systems, devices and methods of the present invention can be configured to measure one or multiple (idealized) points 35 or target areas 35. Throughout the description, the terms point 35, target point 35 and target area 35 can be used interchangeably. It will be understood that practically it may not be possible to measure an idealized point 35, but rather a target area 35 can be measured.

[0288] The measuring device 10 can be configured to perform a measurement by emitting a measurement signal along the measurement path 15 and receiving a received portion of the measurement signal. The measuring device 10 can be configured to measure an amplitude and phase of the received portion. The received portion can comprise a transmitted part and a reflected part (illustrated in Figs. 4a and 4b). The measuring device can be configured to determine a transmission property and / or a reflection property of the target area.

[0289] The measuring system can be configured to perform, with the measuring device, a plurality of measurements for a plurality of measurement paths 15, to thereby obtain a measured data set. For at least some of the measurements, the respective measurement paths 15 intersect the target area 15 at different incidence angles 13.

[0290] In some embodiments, measurement paths 15 with different incidence angles 13 can be created by generating a relative motion between the measuring device 10 and the target area 35. Said relative motion can comprise a rotational motion of the measuring device 10 and / or of the device under test 30. In such embodiments, a positioning system 40 can be used.

[0291] Alternatively or additionally, measurement paths 15 with different incidence angles 13 can be created by providing multiple antenna pairs 12, 14, each defining a respective measurement path 15 with a different incidence angle. This is illustrated in Fig. 3.

[0292] Referring to Fig. 1, a relative motion between the measuring device 10 and the target area 35 can be generated. Said relative motion can be generated using the positioning system 40 - e.g., as illustrated by the double arrows in Fig. 1. For example, the relative motion can be generated by rotating the measuring device 10 with respect to an axis perpendicular to the measurement path 15. This can be done using, for example, a linear stage 40 or robotic arm 40, to which the measuring device 10 can be fixed. Alternatively or additionally, the relative motion can be generated by rotating device under test 30- e.g., as illustrated by the double arrows in Fig. 1. For example, the relative motion can be generated by rotating the device under test 30 with respect to an axis perpendicular to the measurement path 15. This can be done using for example a linear stage 40 or a robotic arm 40 to which the device under test 30 can be fixed. The relative motion can also be generated by moving both the target area 35 and the measuring device 10. Alternatively or additionally, the relative motion can be generated using indirect motions such as oscillations or vibrations of the target area 35 caused for example by the material properties of the target area 35 and a previous motion.

[0293] Changing the relative position between the measuring device 10 and the target are 35 can cause the incidence angle 13 between the measurement path 15 and the target area 35 to change.

[0294] In a preferred embodiment, the transmitter 12 and the receiver 14 can be horn antennas 12, 14. The horn antennas can be advantageous due to their substantial directivity which can facilitate directing the emitted electromagnetic waves toward a preferred direction, such as, along the measurement path 15. Further, a horn antenna 12, 14 can also be advantageous as it can allow a gradual transition structure, realizing impedance matching with open air and thus allowing for efficient emission / reception of the electromagnetic waves.

[0295] Furthermore, horn antennas 12, 14 can emit linearly polarized electromagnetic waves. For example, it can be advantageous to match the polarization of the transmitter 12 and receiver 14 with the polarization of the radar that will be covered by the DUT - in this case the DUT being a radome. This can allow for more accurate results to be obtained based on the rationale that the more similar the test conditions are to the real conditions the more accurate results can be obtained. A radar can be configured to transmit electromagnetic waves with different polarizations, such as, linear (horizontal or vertical), circular (clockwise or anti-clockwise), epileptic, etc. However, in most cases, radar sensors are configured to emit electromagnetic waves with linear polarization. Thus, the utilization of horn antennas 12, 14 can be advantageous for testing radomes of radars that emit linearly polarized electromagnetic waves.

[0296] As discussed, the measuring system can comprise a data processing system 20, which can also be referred to as a processing system 20 for the sake of brevity. The processing system 20 can comprise one or more processing units configured to carry out computer instructions of a program (i.e., machine readable and executable instructions). The processing unit(s) can be singular or plural. For example, the processing system 20 may comprise at least one of CPU, GPU, DSP, APU, or FPGA. The processing system 20 can comprise memory components, such as main memory (e.g., RAM), cache memory (e.g., SRAM) and / or secondary memory (e.g., HDD, SDD). The processing system 20 may comprise volatile and / or non-volatile memory such an SDRAM, DRAM, SRAM, Flash Memory, MRAM, F-RAM, or P-RAM. The processing system 20 can comprise internal communication interfaces (e.g., busses) configured to facilitate electronic data exchange between components of the data processing system 20, such as the communication between the memory components and the processing components. The data processing system 20 can comprise external communication interfaces configured to facilitate electronic data exchange with devices external to the data processing system 20. The data processing system 20 can be configured for wired and / or wireless data communication. For example, the processing system 20 can be configured to transfer electronic data using a standardized communication protocol. For example, the data processing system can comprise a network card and / or a USB port. The processing system 20 can comprise a system-on-chip comprising processing units, memory components and busses.

[0297] The processing system 20 may be a centralized or distributed computing system. In some embodiments, the processing system 20 may be external to the measuring device 10. Alternatively, the processing system 20 and the device 10 may be integrated into a single device. For example, the measuring device 10 may comprise the processing system 20.

[0298] The processing system 20 can facilitate automating the operations of the measuring device 10 and / or of the measuring system. That is, the processing system 20 may control the measuring device 10 such that the measurements of the target area 35 and / or the relative motions are performed automatically. The processing system 20 can be operatively connected to other components. More particularly, processing system 20 may be operatively connected to the measuring device 10 (e.g., to the transmitter 12 and to the receiver 14) and / or to the positioning system 40. The term operatively connected can refer to wired or wireless connections configured for electronic data exchange, such as, control signals.

[0299] The processing system 20 can be connected with the transmitter 12 by a transmitter connector 22. Thus, the processing system 20 can trigger the transmitter 12 to emit an electromagnetic wave with a preset pattern in time and frequency. For example, the processing system 20 can trigger the transmitter 12 to emit electromagnetic waves with a preset bandwidth centred around a preset frequency. The processing system 20 can trigger the transmitter 12 to emit electromagnetic waves within the range of frequencies and bandwidths supported by the transmitter 12 (i.e., based on the geometry or physical structure of the transmitter 12 a certain range of frequencies can be transmitted efficiently).

[0300] Similarly, the processing system 20 can be connected with the receiver 14 by a receiver connector 24. Thus, the processing system 20 can receive signals provided by the receiver 14 and / or data indicative of the signal sensed by the receiver 14. The processing system 20 can be configured to identify signal reception by the receiver 14 (or alternatively identify when the receiver 14 is simply "listening" to background noise). The differentiation of signal reception (i.e., reception of the signal that is transmitted by the transmitter 12) from background noise (and / or interference) at the receiver 14 can be done using power squelching - i.e., only signals above a certain power level can be considered as signal reception, while the rest is considered as background noise. When a signal reception is identified, the processing system 20 can use information regarding the transmitted signal and information regarding the receiving signal to measure dielectric properties of the medium(s) between the transmitter 12 and receiver 14.

[0301] The transmitter connector 22 and receiver connector 24 can be electrical conductors 22, 24, such as, wires 22, 24, preferably coaxial cables 22, 24. In such embodiments, the processing system 20 can trigger the transmitter 12 by sending an electrical signal through the conductor 22. The transmitter 12 can then convert the electrical signals into electromagnetic radiation. The receiver 14 can convert electromagnetic radiation into electrical signals, which can then be transmitted through the conductor 24 to the processing system 20.

[0302] Alternatively, the transmitter connector 22 and receiver connector 24 can be waveguides 22, 24. In such embodiments, the processing system 20 can be configured to trigger the transmitter 12 by generating electromagnetic waves and transmitting those through the waveguide 22 to the transmitter 12. The transmitter 12 can be configured as an interface between the waveguide 22 and open-air for an efficient transmission of the waves. The receiver 14 can similarly provide an interface between open-air and the waveguide 24, allowing electromagnetic radiation to be received and transmitted through the waveguide 24 to the processing system 20.

[0303] The processing system 20 can further be operatively connected with the positioning system 40 via a positioning system connector 26. Thus, the processing system 20 can trigger the positioning system 40 to generate a relative motion between the target area 35 and the measuring device 10. For example, the processing system 20 can trigger the positioning system 40 to generate the relative motion with a preset pattern, e.g., with one or more preset velocities and / or with one or more preset durations. The positioning system connector 26 can be configured for electronic data exchange between the processing system 20 and the positioning system 40. This can allow the processing system 20 to provide instructions to the positioning system 40 and / or the positioning system 40 to provide status data to the processing system 20. Status data can for example indicate the incidence angle between the measurement path 15 and the target area 35.

[0304] In some embodiments, the received portion of the measurement signal can be provided to the processing system 20 in the same frequency range as transmitted from the transmitter 12 and received by the receiver 14. In other words, the received portion of the measurement signal can be provided to the processing system 20 in the radio-frequency (RF) range. Similarly, the processing system 20 can provide the signal to the transmitter 12 in the RF range. Put differently, the measurement signal may not undergo any frequency conversion between the processing system 20 and the transmitter 12 and between the processing system 20 and the receiver 14.

[0305] Alternatively, the measuring system can comprise a respective frequency converter for the transmitter 12 and for the receiver 14. More particularly, the measuring system and in particular the measuring device 10 can comprise an up-converter that can be used between the processing system 20 and the transmitter 12 and a down-converter that can be used between the receiver 14 and the processing system 20. Thus, the processing system 20 can operate at an intermediate frequency IF (e.g., 1 - 6 GHz) or at baseband (0 - 3 GHz), while the transmitter 12 and receiver 14 can transmit and / or receive RF signal at higher frequencies (i.e., radio frequency range, e.g., 20 - 160 GHz). This can be advantageous as the processing system 20 can be configured to operate at a certain low frequency range (e.g., IF range or baseband) independent of the RF range of the signals transmitted between the transmitter 12 and receiver 14.

[0306] In some embodiments a surface of the up-converter facing the receiver 14 can form (at least a part of) the first reflecting component 17T. Alternatively or additionally, a surface of the down-converter facing the transmitter 12 can form (at least a part of) the second reflecting component 17R.

[0307] The processing system 20 can be configured to control the measuring system and / or to carry out particular method steps for determining at least one property of a target area 35 of the DUT. For example, the processing system 20 can be configured to carry out step S4 of the method illustrated in Fig. 5.

[0308] The measuring device 10 can be configured to carry out step S2 and S3 of the method illustrated in Fig. 5.

[0309] In general, the measuring system can be configured to carry out the method according to the method illustrated in Fig. 5.

[0310] Figs. 2a to 2c illustrate different measurement paths 15 defined by an antenna pair 12, 14. The illustrated measurement paths 15 intersect the target area 35 of the device under test 30 at difference incidence angles 13.

[0311] In Fig. 2a, the measurement path 15 is perpendicular with the target area 35. The incidence angle 13 is therefore 90°. In Fig. 2b, the relative position between the measuring device 10 and the target area 35 has been changed. This can be done by generating a relative motion between the measuring device 10 and the target area 35. The relative motion can, for example, be generated by the positioning system 40 (shown in Fig. 1). For example, the measuring device 10 and / or the device under test 40 can be tilted. Therefore, the incidence angle 13 can be changed.

[0312] Similarly, in Fig. 2c, the relative position between the measuring device 10 and the target area 35 has been changed. This can be done by generating a relative motion between the measuring device 10 and the target area 35. The relative motion can, for example, be generated by the positioning system 40 (shown in Fig. 1). For example, the measuring device 10 and / or the device under test 40 can be tilted. The tilting in Fig. 2c is opposite to the tilting in Fig. 2b. Therefore, the incidence angle 13 can be changed.

[0313] It will be understood that generating a relative motion is not necessary to create measurement paths 15 with different incidence angles.

[0314] As illustrated in Fig. 3, in some embodiments the measuring device 10 may comprise multiple antenna pairs 12, 14. In the example of Fig. 3, the measuring device 10 comprises 3 antenna pairs 12, 14, indexed 1 to 3. However it will be understood that the measuring device can comprise any number of antenna pairs.

[0315] Therefore, the measuring device 10 illustrated in Fig. 3 can comprise several measurement paths 15-1, 15-2 and 15-3 intersecting the target area 35 at different incident angels.

[0316] The antenna pairs 12, 14 may either use different frequencies and / or may use different time intervals to perform the measurements. This way interference between the antenna pairs 12, 14 can be alleviated.

[0317] The length of the measurement paths 15 of the multiple antenna pairs 12, 14 can be known in advance. This can facilitate compensating for the different lengths of the measurement paths 15 when performing the measurements. In some embodiments, the measuring device 10 can be configured such that the measurement paths 15 of different antenna pairs 12, 14 comprise identical lengths.

[0318] Figs. 4a and 4b illustrate transmitted and reflected pats of the measurement signal that can be comprised by the received portion. Not to overload Figs. 4a and 4b the referral numbers have been omitted.

[0319] The received portion of the measurement signal may comprise a transmitted part. The bold arrow P0 illustrates a transmitted part of the measurement signal. The transmitted part follows a direct path from the transmitter, through the target area 35 and to the receiver 14. The path followed by the transmitted part can be the shortest path that the measurement signal can follow before being received by the receiving antenna 12. It can comprise a length equal to the distance between the antennas 12, 14. The path of the transmitted part of the measurement signal and the measurement path can be coincident, at least outside the target area 35.

[0320] The received portion of the measurement signal may further comprise reflected parts of the measurement signal. The reflected part can comprise a first reflection (illustrated by the dotted arrow Pl) that is reflected by the first side 32 of the target area 35, then by at least one first reflecting surface of or near the transmitter 12, then are transmitted through the target area 35 and received by the receiver 14.

[0321] The reflected part can comprise a second reflection (illustrated by the dotted arrow P2) which is transmitted through the target area 35 first, reflected by at least one second reflecting surface 17R (see Fig. 1) of or near the receiving antenna 55R, then is reflected by the second side 34 of the target area 35 and received by the receiver 14.

[0322] It will be understood that reflections following other paths can also be received by the receiver 14. Fig. 4b illustrates, as an example, two other reflections Pl' and P2' - which can be referred to as second-degree reflections - because they are reflected twice by the target area 35. In particular, the second-degree reflection Pl' is similar to the first reflection Pl and differs only in that the reflection bounces between the transmitter 12 and the first side 32 two times before transmitting through the target area 35. Similarly, the second-degree reflection P2' is similar to the second reflection P2 and differs only in that the reflection bounces between the second side 54 two times before being received by the receiver 14.

[0323] Fig. 5 depicts a flowchart of a method for measuring a target area of a device under test.

[0324] In SI, the method can comprise providing a measuring device 10. The measuring device 10 can comprise any of the features discussed above and below with respect to the other Figures. In particular, the measuring device 10 can be configured to perform a measurement by emitting a measurement signal along a measurement path 15 and receiving a received portion of the measurement signal.

[0325] In S2 and S3, the method can comprise with the measuring device 10, performing a plurality of measurements for a plurality of measurement paths 15, respectively, to thereby obtain a measured data set, wherein for at least some of the measurements, the respective measurement paths 15 intersect the target area 35 at different incidence angle. The measurement paths 15 intersecting the target area 35 at different incidence angles can be created via a relative motion between the measuring device 10 and the target area 35, as for example illustrated in Fig. 2. Alternatively or additionally, the measurement pats 15 measurement paths 15 intersecting the target area 35 at different incidence angles can be created by providing a measurement device 10 with multiple antenna pairs 12, 14 - as for example illustrated in Fig 3.

[0326] In S4, the method can comprise with a data processing system 20 (see Fig. 1), determining at least one layer-parameter of the target area 35 based on the measured data set. Each layer-parameter can be indicative of a layer-property of the target area 35. In S4 the method can comprise determining a number of layers of the target area 35, respective thickness of each of at least one layer of the target area 35 and / or a respective dielectric property of each of at least one layer of the target area. Said dielectric property can be a permeability and / or a permittivity of the respective layer.

[0327] In some embodiments, the method can comprise determining at least one target area parameter, wherein each target area parameter is indicative of an end-to-end property of the target area (35).

[0328] Fig. 6 depicts an embodiment of the measuring device 10, comprising a clamp structure 60 (also referred to as a clamp 60). The clamp 60 can comprise a base frame 66, a first mount 62 and a second mount 64. The first mount 62 can be referred to as a first antenna mount 62. Similarly, the second mount 64 can be referred to as a second antenna mount 64.

[0329] The first mount 62 and the second mount 64 can extend from the same side of the base frame 66. That is, the first mount 62, the second mount 64 and the base frame 66 can form a substantially U-shaped structure of the clamp structure 60.

[0330] In some embodiments, the clamp 60 can be manufactured by attaching or fixating the first mount 62 and the second mount 64 on two opposing sides of the base frame 66. Alternatively, the clamp 60 can be manufactured as a single part - i.e., without mounting or assembling or attaching smaller parts together to form the clamp 60.

[0331] The clamp 60 can provide a stable structure for the transmitter 12 and receiver 14 to be mounted. As discussed, it can be advantageous to have the transmitter 12 and the receiver 14 aligned with each-other such that most of the radiated electromagnetic waves emitted by the transmitter 12 can be received by the receiver 14. The shape of the clamp structure 60 can facilitate this alignment. Further, it can be advantageous that the distance between the two antennas 10 to be kept constant. The clamp structure 60, more particularly the base frame 66, can facilitate keeping the distance between the transmitter 12 and receiver 14 constant.

[0332] The clamp structure 60 can further facilitate the handling of the transmitter 12 and the receiver 14, without changing the relative position between the transmitter 12 and the receiver 14.

[0333] The clamp structure 60 can also be configured to allow the fixation of the antenna mounts 62 and 64 on different parts of the base frame 66. This can allow the adjustment of the relative position between the two antenna mounts 62 and 64, such as, the adjustment of the distance between the antenna mounts 62 and 64. For example, the base frame 66 can comprise multiple attaching elements (not shown), wherein the antenna mounts 62 and 64 can be attaching to the base frame 66.

[0334] Whenever a relative term, such as "about", "substantially" or "approximately" is used in this specification, such a term should also be construed to also include the exact term. That is, e.g., "substantially straight" should be construed to also include "(exactly) straight".

[0335] Whenever steps were recited in the above or also in the appended claims, it should be noted that the order in which the steps are recited in this text may be accidental. That is, unless otherwise specified or unless clear to the skilled person, the order in which steps are recited may be accidental. That is, when the present document states, e.g., that a method comprises steps (A) and (B), this does not necessarily mean that step (A) precedes step (B), but it is also possible that step (A) is performed (at least partly) simultaneously with step (B) or that step (B) precedes step (A). Furthermore, when a step (X) is said to precede another step (Z), this does not imply that there is no step between steps (X) and (Z). That is, step (X) preceding step (Z) encompasses the situation that step (X) is performed directly before step (Z), but also the situation that (X) is performed before one or more steps (Yl), ..., followed by step (Z). Corresponding considerations apply when terms like "after" or "before" are used.

[0336] While in the above, a preferred embodiment has been described with reference to the accompanying drawings, the skilled person will understand that this embodiment was provided for illustrative purpose only and should by no means be construed to limit the scope of the present invention, which is defined by the claims.

Claims

Claims1. A method for measuring a target area (35) of a device under test (30), comprising providing a measuring device (10) configured to perform a measurement by emitting a measurement signal along a measurement path (15) and receiving a received portion of the measurement signal; with the measuring device (10), performing a plurality of measurements for a plurality of measurement paths (15), respectively, to thereby obtain a measured data set; wherein for at least some of the measurements the respective measurement paths (15) intersect the target area (35) at different incidence angle.

2. The method according to the preceding claim, wherein the measuring device (10) comprises at least one antenna pair (12, 14), wherein each antenna pair (12, 14) comprises a transmitter (12) and a receiver (14) and wherein each antenna pair (12, 14) defines a respective measurement path (15).

3. The method according to the preceding claim, wherein the measuring device (10) comprises a plurality of antenna pairs (12, 14) respectively defining at least some of the measurement paths (15) that intersect the target area (35) at different incidence angles.

4. The method according to any of the preceding claims, wherein the method comprises generating a relative motion between the measuring device (10) and the target area (35) to define at least some of the measurement paths (15) that intersect the target area (35) at different incidence angles.

5. The method according to any of the preceding claims, wherein the target area comprises multiple layers stacked on top of each other and wherein the method comprises, with a data processing system, determining at least one layer-parameter of the target area (35) based on the measured data set.

6. The method according to the preceding claim, wherein one layer-parameter is indicative of a number of layers of the target area.

7. The method according to any of the 2 preceding claims, wherein one layerparameter is indicative of a respective layer thickness of at least one layer of the target area (35).

8. The method according to any of the 3 preceding claims, wherein one layerparameter is indicative of a respective layer electromagnetic property of at least one layer of the target area (35).

9. The method according to any of the 4 preceding claims, wherein the method comprises obtaining, using a data processing device and from a memory, a computer model of the target area; wherein said computer model comprises model parameters indicative of layer properties of the target area; wherein the computer model is configured to digitally replicate a measurement by receiving as input data indicative of a measurement signal incident on the target area and calculate an output indicative of an expected received portion of the measurement signal; wherein the method comprises determining the at least one layer-parameter based on the computer model.

10. The method according to the preceding claim, wherein the output of the computer model is indicative of an expected measured data set; the input to the computer model is configured to characterize, at least in part, the measurement signal incident on the target area and the model parameters comprise information related to layer properties of the target area.

11. The method according to any of the 2 preceding claims, wherein the input to the computer model comprises a frequency, an amplitude, a polarization and / or an incidence angle of the measurement signal.

12. The method according to any of the 3 preceding claims, wherein the model parameters comprise information related to layer thicknesses, layer permittivities, layer permeabilities and / or number of layers within the target area.

13. The method according to any of the 4 preceding claims, further comprising optimizing the model parameters such that the output of the computer model fits with the measured data set and wherein determining the at least one layer-parameter based on the computer model comprises determining the at least one layer-parameter based on the optimized model parameters.

14. The method according to any of the preceding claims, wherein the measuring device (10) comprises a clamp structure (60) and wherein the clamp structure (60) comprises a first mount (62) configured for mounting at least one transmitter (12); a second mount (64) configured for mounting at least one transmitter (14); a base frame (66) and wherein the first mount (62) and the second mount (64) extend from the same side of the base frame (66).

15. A system for measuring a target area (35) of a device under test (30), comprising a measuring device (10) configured to perform a measurement by emitting a measurement signal along a measurement path (15) and receiving a received portion of the measurement signal; the measuring device (10) configured to perform a plurality of measurements for a plurality of measurement paths (15), respectively, to thereby obtain a measured data set; wherein for at least some of the measurements the respective measurement paths (15) intersect the target area (35) at different incidence angle; wherein the system is configured to carry out the method according to any of the preceding claims.

Images