Method and device for contactless measurement of an electric field distribution

Abstract

Method for the contactless measurement of an electric field distribution of an electronic component (15) to be examined, wherein microwave signals are emitted or transmitted by the electronic component (15) to be examined and are received by an antenna device (10) which comprises a plurality of individual antennas (11) with an aperture width (D), characterized in that a distance (L) between the antenna device (10) and the electronic component (15) to be examined is selected to be greater than 3 times the wavelength of the received microwave signals and less than one third of the aperture width (D).

Description

[0001] The invention relates to a method and a device for contactless measurement and, if appropriate, representation of an electric field distribution in an electronic component to be examined, wherein microwave signals are emitted and / or transmitted by the electronic component to be examined and are detected by an antenna device.

[0002] The electromagnetic signals emitted or transmitted by a device, particularly in the microwave range, are measured for a wide variety of purposes. Before they are approved, mobile radio devices are tested for their radiated transmission power and propagation characteristics. The radiated microwave signals are primarily in the operating frequency range of such mobile radio systems, which lies in a frequency range of, for example, approximately 800 MHz to 2.6 GHz. Similar tests are also carried out for devices and components in high-frequency technology. In the development of integrated circuits, particularly in the high-frequency range, measurements of electric field distribution are helpful for detecting faults in the circuits. Direct measurement of the high-frequency cables is associated with large errors and is therefore of little use, since mechanical contact strongly influences the signal to be measured.

[0003] US 2011 / 0193566 A1 describes a contactless multi-channel near-field measurement system for measuring, testing, and verifying the operating parameters of such electromagnetically radiating components. The near field of electromagnetic radiation sources on the component under test is detected using an antenna array, and a far-field distribution of the electromagnetically radiating component is calculated from this. During the measurement, the component under test is positioned at a distance from the antenna array that is only half to one hundredth of the wavelength λ of the emitted microwave signal.

[0004] Since the near field of a microwave radiation source is strongly influenced by environmental influences from surrounding structures, the measured signals contain interference, for example, due to reflections or dynamic coupling between individual antenna elements and the component under investigation. These interferences are evaluated by a processing unit and taken into account through complex correction measures when generating the near-field distribution. From this corrected near-field distribution, the far-field distribution of the radiation source is determined using a transformation.

[0005] These correction measures, as well as the transformation from the near field to the corresponding far field, require significant computational effort and thus require very powerful processors and are associated with longer analysis times. Another disadvantage is that residual interference in the signals distorts the measurement results.

[0006] US 2009 / 0237092 A1 describes a sensor array with a plurality of modulated slits for microwave and / or millimeter wave imaging. The positions of the slits in the array define a spatial area at the distance of an object for detecting the object's electric field. Each of the slits outputs a signal representative of the measured field and the position of the slit. A processor decodes the signals and generates an image of the object.

[0007] US 2007 / 0024293 A1 describes a method and device for electromagnetic measurement.

[0008] EP 1174722 A1 describes a probe for electromagnetic wave sources.

[0009] EP 1347303 A2 describes an automatic design and layout of electronic devices and systems taking into account electromagnetic compatibility.

[0010] It is therefore the object of the present invention to provide a method and a device for the contactless measurement and representation of electric field distributions in which hardly any or no mutual coupling effects occur and which enable an accurate determination of the electric field in the plane of the component to be examined in a short time and allow a localization of a radiation source with high spatial resolution.

[0011] The object is achieved by the method according to the invention with the features of claim 1 and the device with the features of claim 10. Advantageous developments of the method according to the invention and the device according to the invention are presented in the subclaims.

[0012] In the method according to the invention for the contactless measurement of an electric field distribution in the plane of an electronic component to be tested, microwave signals are emitted or transmitted by the electronic component to be tested and received by an antenna device comprising a plurality of antennas spanning an aperture width D. A distance L between the antenna device and the electronic component to be tested is selected to be greater than three times the wavelength of the measured microwave signals and less than one-third of the aperture width D.

[0013] At the specified distance L, coupling effects and reflections between the antennas or between the antenna device and the component under test are negligible, so that only the far field of a radiation source in the component under test is detected. Consequently, there is little or no corresponding interference in the measured signal, eliminating the need for computationally intensive and time-consuming correction calculations during evaluation. The signals measured by the antenna device can be used directly to determine the field distribution.

[0014] It is particularly advantageous to determine the electric field distribution (distribution of the electric field) in the plane of the electronic component by back-calculating the signal propagation to the signal source using a near-field imaging algorithm, such as a modified backprojection algorithm. These algorithms provide a good representation of the electric field distribution in the plane of the component to be measured, especially for measurements in the aforementioned distance range.

[0015] It is advantageous if the emitted or transmitted microwave signal is additionally received by a stationary reference antenna and used to correlate the phase with the microwave signals measured at the antenna device. For the back calculation of the electric field in the plane of the component under investigation, it is advantageous that the microwave radiation emitted by or transmitted through the component under investigation is as coherent as possible. By using a stationary reference antenna, the field distribution of a periodically changing radiation source or a pulsed radiation source can also be back calculated. Likewise, the reference signal received by the stationary reference antenna enables the use of an antenna device that consists, for example, of a linear antenna array and spans an aperture through mechanical movement.This makes it possible to correlate the phase of the microwave signal emitted by the component under investigation, which is detected by the reference antenna on the one hand and measured by a one-dimensional antenna array or the individual antennas in a specific position on the other.

[0016] It is also advantageous if microwave signals are measured at a predetermined frequency or sequentially at several frequencies within a predetermined frequency range. A preliminary measurement across a wide frequency range identifies a primary frequency that radiates with high intensity. By subsequently measuring the microwave signals at this primary frequency, the electric field distribution can be reliably determined with a single measurement, providing a very timely visual representation of the field distribution. This enables rapid troubleshooting or can be used to verify changes in the field distribution over time.

[0017] For relatively weak microwave signals emitted or transmitted by the component to be measured, it is advantageous to measure several frequencies within a predetermined frequency range in consecutive measurements. For example, by averaging or summing the various measurements, sufficient information can be collected even at low signal strengths, allowing an accurate representation of the field distribution to be created.

[0018] In addition, depth resolution can be achieved by measuring at multiple frequencies. To achieve this, it is advantageous to determine the magnitude of the electric field distribution measured at one frequency and add the magnitudes of the electric field distributions at different frequencies.

[0019] It is also advantageous if the measurement of the microwave signals is triggered by detecting the predetermined measurement frequency in the reference signal. This ensures that a measurement is only performed when a corresponding microwave signal is present, for example, with sufficient power or at a desired frequency, thus ensuring an accurate and reliable result for every measurement.

[0020] It is also advantageous to measure the microwave signals simultaneously at multiple frequencies. This allows sufficient signals to be detected, even with lower-power microwave signals, to reconstruct the electric field distribution. For stronger microwave signals, a single measurement can thus produce a representation with depth of field, i.e., resolution in the z-direction.

[0021] The device according to the invention for the contactless measurement of an electric field distribution of an electronic component comprises an antenna device formed from a plurality of antennas spanning an aperture with an aperture width D and suitable for receiving microwave signals. It further comprises an evaluation unit for implementing an evaluation algorithm. The distance L between the component to be examined and the antenna device is greater than three times the wavelength of the measured microwave signals and less than one-third of the aperture width D. Surprisingly, with the specified ratio between aperture width D and distance L, the measured microwave signals hardly exhibit any interference due to coupling effects. This allows the electric field distribution to be calculated at the level of the component to be examined with very good resolution.

[0022] It is advantageous if the antenna device is designed as a two-dimensional antenna array or as a one-dimensional antenna array that spans an aperture through mechanical movement. A two-dimensional antenna array enables simultaneous measurement of the microwave radiation within the aperture. This allows even temporally non-coherent or transmissive components to be measured without additional devices, such as a reference antenna. A one-dimensional antenna array can be operated with less fast and complex control and readout devices and is therefore more cost-effective. Nevertheless, an antenna device with a large aperture width D can be achieved simply through mechanical movement.

[0023] Embodiments of the method and device according to the invention are illustrated by way of example in the drawings and are explained in more detail in the following description. They show: Fig. 1 shows a first embodiment of a device according to the invention with a component to be examined that emits microwave signals, in a schematic representation; Fig. 2 shows a second embodiment of a device according to the invention with a one-dimensional antenna array as antenna device in a schematic representation; Fig. 3 a third embodiment of a device according to the invention with a component to be examined that transmits microwave signals in a schematic representation and Fig. 4 a representation of the microwave signals measured according to the method and with the device according to the invention as well as the electric field distribution calculated therefrom in the plane of the component to be examined.

[0024] Corresponding parts are provided with the same reference numerals in all figures.

[0025] Based on the Fig. 1, the method according to the invention and a corresponding device are explained. The device comprises an antenna device 10 with a plurality of antennas 11 arranged in a plane, for example, parallel to the component to be examined. A two-dimensional arrangement in the form of an antenna array 20 is shown in Fig. 1 by the dotted lines. The antenna device 10 thus has an aperture 14 with an aperture width D. For example, in a square antenna device 10, the aperture width D corresponds approximately to one side length of the antenna device 10. Each individual antenna 11 is designed, for example, as a horn antenna and is suitable for detecting microwave signals, e.g., in the range between 100 MHz and 1 THz, in particular in a range from 800 MHz to 100 GHz.

[0026] The antenna device 10 is connected to an evaluation unit 12 and a display unit 19, which reads the measured microwave signals from the antenna device 10 and, with the aid of an implemented mapping algorithm, determines the electric field distribution in a measurement plane 18. The evaluation unit 12 and display unit 19 can be implemented as separate units or integrated, as shown.

[0027] In the exemplary embodiment, a reference antenna 13 is also connected to the evaluation and display unit 12. The reference antenna 13 is either designed as a separate antenna, which is arranged, for example, in the immediate vicinity of the antenna device, or a selected individual antenna 11 of the antenna device 10 can be used as the reference antenna.

[0028] A component 15 to be examined is arranged in a measurement plane 18, which is aligned approximately parallel to the aperture 14 of the antenna device 10. The measurement plane 18 or the component 15 to be examined is located at a distance L from the antenna device 10.

[0029] The distance L between the antenna device 10 and the electronic component 15 to be measured is selected to be greater than three times the wavelength, and particularly preferably greater than five times the wavelength, of the measured microwave signals. Coupling effects between the antenna and detector decrease significantly with increasing distance L. At the same time, the distance L is selected to be less than one-third of the aperture width D, so that a spherical wavefront of the electric field can be assumed in the imaging algorithm.

[0030] A typical component 15 to be examined is, for example, an integrated circuit on a printed circuit board with microwave-conducting structures 16 or another microwave-conducting unit. Microwave elements, such as filters or amplifiers, or other radiating elements, emit microwave signals. This applies particularly to faulty or poorly tuned microwave elements.

[0031] The antenna device 10 detects a complex-valued field distribution present at a distance L from the microwave radiation source 17. A measurement is taken at a single manually selected frequency or at a number of different frequencies within a frequency range one after the other, or signals with frequencies within a frequency range are detected simultaneously. Both the magnitude and the phase of the signal are measured.

[0032] In order to extract the electric field distribution in the measurement plane 18, in which the component 15 to be examined is located, from the measured data, the measured complex-valued signal is calculated using a mapping algorithm, which is derived, for example, from a so-called backprojection algorithm. This backpropagation algorithm contains adapted filter techniques to correlate the measured wavefronts. A preferred mapping algorithm in the spatial domain is R(xo,yo,zo,f)=∑∀x∑∀y(M(x,y,f,tn)P(f,tn)⋅exp(+j2πc0f⋅Δr)) with Δr=(x−xo)2+(y−yo)2+zo2

[0033] In this case, R is the electric field distribution of an object cell of the component to be examined at the corresponding coordinates (x0, y0, z0) in the plane of the radiation source 17, f is the frequency, M the measured data of the measured electric field obtained from a single antenna 11 at the position (x, y) in the plane of the aperture at a frequency f at the time of measurement t n was measured, P(f,t n ) the reference signal measured at the reference antenna 13, which at the same time t n how the measured values ​​of the electric field M were measured, Δr is the relative geometric distance between a measuring location (x, y) in the antenna device and an object cell to be examined at the location (x0, y0, z0) in the measuring plane 18, z0 is the distance between the antenna device 10 and the component 15 to be examined and c0 is the speed of light.

[0034] If the measurement duration is less than the coherence duration of the measured microwave signal, the measurement of a reference signal by the reference antenna 13 is not necessary and the term P(f,t n) results in 1 and is therefore eliminated. This is also the case when using a two-dimensional antenna array, as in Fig. 1, is the case due to the simultaneous measurement in the entire aperture.

[0035] For temporally pulsed signals, the reference antenna preferably monitors the spectral line of the signal in order to trigger the measurement by the antenna device 10 when it occurs. Alternatively, the antenna device 10 continuously measures the microwave signal emitted by the component 15 under investigation. Only then are the available data or the images already evaluated and displayed selected.

[0036] A more suitable form of the mapping algorithm for implementation in the evaluation and display unit 12, 19 is its representation in the space-frequency domain as R(xo,yo,zo,f)=FT2D−1(FT2D(M(x,y,f,tn)P(f,tn))⋅exp(−j2πc0f⋅zo)) This refers to FT 2D a two-dimensional Fourier transform with respect to the spatial dimensions x and y of the measured data, FT -1 2D a two-dimensional inverse Fourier transform with respect to the wavenumber k x in dimension x and wavenumber k y in dimension y, z0 is the distance between the antenna device 10 and the component to be measured 15 or the measuring plane 18, k x the x-component of a wavenumber vector present at the position x of the antenna device 10 and k y the y-component of the wavenumber vector present at the location y of the antenna device 10.

[0037] A spatial resolution Δ of Δ=λDL2+(D2)2 be achieved, whereby L is the distance between the antenna device 10 and the measuring plane 18 of the component 15 to be examined and D is the aperture and λ is the wavelength of the microwave radiation under investigation.

[0038] If the distance L is small compared to the aperture width D, L can be neglected and the spatial resolution Δ is Δ=λ2

[0039] By optimizing the backpropagation algorithm to utilize coherence, the resolution can be improved by a factor of 2 to 4. For microwave signals of 30 GHz, for example, a resolution of approximately 2.5 mm can be achieved.

[0040] Fig. Figure 2 shows a second embodiment of the measuring device. The antenna device 10 comprises a one-dimensional antenna array 21, which is mechanically moved in the direction of the solid arrow and thus defines an aperture 14. An aperture 14 can also be achieved by rotating the one-dimensional antenna array 21, for example, around a point in the center of the longitudinal alignment or around an edge point in the longitudinal alignment. The antenna device 10 can also have an aperture in the form of a partial cylinder shell or in the form of another curved plane, in Fig. 1 and Fig. 2 which can be formed by either a one-dimensional or a 2-dimensional antenna array.

[0041] The emitted microwave signals, in Fig. 1 and Fig. 2, indicated by the dashed arrows, emerge, for example, at a damaged area 17 of a housing 21 and are received by the antenna device 10. The evaluation and display unit 12, 19 receives, in addition to the measurement signal of the antenna device 10, the signals detected by the reference antenna 13 and establishes a correlation with the measurement signals.

[0042] With such an arrangement, a large aperture D can be achieved while still keeping the evaluation capacity and complexity of the antenna circuits low. This allows for large apertures and thus the measurement of microwave signals with long wavelengths.

[0043] Fig. 3 shows a further exemplary embodiment with an antenna device 10 and the connected evaluation and display unit 12, 19 as well as a reference antenna 13. A component 15 to be measured does not emit microwave signals itself, i.e., is not the radiation source itself, but is illuminated by an external radiation source 27, and the antenna device 10 merely receives transmitted microwave signals. The external radiation source 27 is stationary and arranged on the side of the component to be measured facing away from the antenna device 10. The transmittance of the component 15 to be examined is determined, and thus its absorption properties are ascertained. Such a measurement can also be used to locate leaks, cracks or breaks, or even material damage in a housing or circuit board.

[0044] Fig.Figure 4 shows diagrams 30, 31, 32, and 33 of a simulation of the method. A component to be examined is assumed to have two point radiation sources 37, 38 located at the positions marked by the crosses in diagram 30. The point radiation sources 37, 38 emit, for example, microwave signals with a frequency of 24 GHz. Diagram 31 shows the intensity of the electric field received by an antenna device 10 at a distance of 10 cm from the component to be examined. Diagram 32 accordingly shows the phase of the electric field measured by the antenna device 10. The grayscale indicates the values ​​of the measured signals according to the legend shown to the right of the diagram. By applying the mapping algorithm, a representation 33 of the electric field distribution in the measurement plane 18, i.e., in the plane of the component 15 to be examined, can be calculated and displayed.

[0045] The two radiation sources shown in Figure 30 can be localized and displayed with a resolution better than 5 mm.

[0046] All described and / or illustrated features can be advantageously combined within the scope of the invention. The invention is not limited to the described embodiments.

Claims

[1] Method for the contactless measurement of an electric field distribution of an electronic component (15) to be examined, wherein microwave signals are emitted or transmitted by the electronic component (15) to be examined and are received by an antenna device (10) comprising a plurality of individual antennas (11) with an aperture width (D), characterized by that a distance (L) between the antenna device (10) and the electronic component (15) to be examined is selected to be greater than 3 times the wavelength of the received microwave signals and less than one third of the aperture width (D). [2] Method according to claim 1, characterized by that the distance (L) between the antenna device (10) and the electronic component (15) to be examined is chosen to be greater than 5 times the wavelength of the received microwave signals. [3] Method according to one of claims 1 or 2, characterized bythat the electric field distribution in a plane (18) of the electronic component is determined by back-calculating the signal propagation to a signal source (17) using a near-field imaging algorithm. [4] Method according to claim 3, characterized by that the emitted or transmitted microwave signals are additionally received by a stationary reference antenna (13) and the microwave signal received at the reference antenna (13) is used as a reference signal for correlating a phase with the microwave signals received at the antenna device (10). [5] Method according to one of claims 1 to 3, characterized by that the microwave signals are measured at a predetermined frequency or are measured successively at several frequencies that lie within a predetermined frequency range. [6] Method according to one of claims 1 to 4, characterized bythat the microwave signals are measured simultaneously at several frequencies. [7] Method according to claim 4, characterized by that a near-field imaging algorithm is used which is given by R(xo,yo,zo,f)=∑∀x∑∀y(M(x,y,f,tn)P(f,tn)⋅exp(+j2πc0f⋅Δr)) with Δr=(x−xo)2+(y−yo)2+zo2 where R is the electric field distribution of an object cell to be examined at the coordinates x0, y0, z0 and the frequency f, M that in the plane x, y at the frequency f and at time t n measured complex electric field, P(f, t n ) the measured reference signal of a reference antenna (13) which is at the same time t n how the electric field was measured, Δr is the relative geometric distance between the antenna device (10) at location x, y and the object cell to be examined at location x0, y0, z0 in the measuring plane (18) of the component to be examined (15) and c0 denotes the speed of light. [8] Method according to claim 7, characterized by that an amount of the determined electric field distribution R, which was measured at different frequencies f, is determined and the amounts of the measured electric field distributions R are added. [9] Method according to one of claims 4, 7 or 8, characterized by that the measurement of the microwave signals is started by detecting a predetermined frequency in the reference signal. [10] Device for contactless measurement of an electric field distribution of an electronic component (15) to be examined, comprising an antenna device (10) with a plurality of individual antennas (11) which span an aperture (14) with an aperture width (D) and which are suitable for receiving microwave signals, and an evaluation unit (12) for carrying out an evaluation algorithm characterized by that a distance (L) between the antenna device (10) and the electronic component (15) to be examined is greater than 3 times the wavelength of the received microwave signals and less than one third of the aperture width (D). [11] Device according to claim 10, characterized by that the distance (L) between the antenna device (10) and the electronic component (15) to be examined is greater than 5 times the wavelength of the received microwave signals. [12] Device according to one of claims 10 or 11, characterized bythat the evaluation unit (12) is designed such that a near-field imaging algorithm can be executed for back-calculating the signal propagation to a signal source (17). [13] Device according to one of claims 10 to 12, characterized by that the antenna device (10) is designed as a 2-dimensional antenna array (20) or as a one-dimensional antenna array (21) which spans the aperture (14) by mechanical movement. [14] Device according to claim 12, characterized by that a reference antenna (13) is arranged in a fixed position with respect to the electronic component (15) and the antenna device (10). [15] Device according to claim 14, characterized by that the evaluation unit (12) is designed such that the evaluation unit (12) executes a near-field imaging algorithm which is given by R(xo,yo,zo,f)=∑∀x∑∀y(M(x,y,f,tn)P(f,tn)⋅exp(+j2πc0f⋅Δr)) with Δr=(x−xo)2+(y−yo)2+zo2 where R is the electric field distribution of an object cell to be examined at the coordinates x0, y0, z0 and the frequency f, M that in the plane x, y at the frequency f and at time t n measured complex electric field, P(f, t n ) the measured reference signal of a reference antenna (13) which is at the same time t n how the electric field M was measured, Δr is the relative geometric distance between the antenna device (10) at location x, y and the object cell to be examined at location x0, y0, z0 in the measuring plane (18) of the component to be examined (15) and c0 denotes the speed of light. [16] Device according to one of claims 10 to 15, characterized by , a display unit (19) for displaying the measured electric field distribution.

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