Antenna characterization using spatial sampling

Abstract

The invention relates to a method for locating and characterizing one or more electromagnetic radiation sources. The method comprises the steps of: measuring one or more electrical signals received from one or more sources placed in an observation area in front of the sampling device; time reversal of the measured one or more electrical signals; inputting the one or more time-inverted electrical signals into an electromagnetic field resolver, the electromagnetic field resolver modeling the sampling device and being configured to solve a Maxwell equation; determining a reconstructed electromagnetic field by operating an electromagnetic field resolver with the one or more time-reversed electrical signals as one or more input signals; identifying one or more focuses in the reconstructed electromagnetic field, thereby locating one or more modeling sources in the simulated observation region; and directly or indirectly obtaining respective far-field radiation patterns of the one or more modeled sources from the reconstructed electromagnetic field.

Description

Technical Field

[0001] The present invention belongs to the field of antenna characterization. More specifically, the present invention relates to a method for locating an electromagnetic source and finding its radiation pattern. The present invention also relates to a corresponding apparatus and system for implementing the method. Background Art

[0002] With the emergence of modern wireless communication systems such as 5G and the Internet of Things (IoT) and the shift to millimeter-wave communication modes, antenna pattern and radiation emission measurements are essential steps in the design and verification process of wireless systems.

[0003] Mechanical raster scanning is currently the most widely used technique for electromagnetic interference (EMI) measurements or antenna source localization, characterization, or far-field pattern measurements, where a positioning robot is used to measure the gain of an antenna source in the far field. In the case of far-field scanning, measurements must be repeated for various incident angles to provide a complete three-dimensional (3D) pattern of the antenna under test. These types of measurements are time-consuming and can also become very complex for narrow-beam and beamforming scenarios. At millimeter wavelengths, achieving precise positioning can also be a challenge.

[0004] Near-field scanning methods developed based on the plane-wave spectrum representation of the electromagnetic field are also used to detect and characterize electromagnetic sources. A two-dimensional (2D) robotic scanner is used to position a probe to measure the field components close to the source surface, and a near-field to far-field transformation is used to reconstruct the antenna pattern. This method can provide very high-resolution results for source detection. However, mechanical scanning is still required, and the influence of the probe and its interaction with the emission source or antenna under test need to be minimized as much as possible.

[0005] Recently, a wired metal lens and compressive sensing have been used together to locate a sound source, which is a technique that breaks through the diffraction limit. However, since the source is placed near the wired metal lens and the metal lens and the source antenna have near-field interaction, the accurate content of the field cannot be recovered due to the near-field interaction. Summary of the Invention

[0006] An object of the present invention is to overcome at least some of the above problems related to locating and characterizing an electromagnetic radiation source and retrieving its radiation pattern. Therefore, the present invention aims to propose a hardware element and a method that can locate and characterize an electromagnetic radiation source such as an antenna and use spatial sampling to retrieve its radiation pattern.

[0007] According to a first aspect of the present invention, there is provided a method for locating and characterizing an electromagnetic radiation source according to claim 1.

[0008] The present invention proposes a new technique for locating and characterizing electromagnetic radiation sources using the concept of spatial sampling. The proposed method allows for very precise location and characterization of the radiation sources without performing any scanning operations of the radiation field. Additionally, the proposed method does not require the use of a large number of sensors or robotic arms and provides fast measurements compared to traditional point-to-point scanning methods. The sampling device used in the proposed method can also be more compact than the devices used in currently known solutions. More specifically, according to the present invention, compared to the minimum distance of 2x D 2 / λ in the current solution, the distance between the source antenna and the front face of the sampling device can be as low as 0.62×sqrt(D 3 / λ), where D represents the maximum size of the source antenna and λ represents the wavelength of the signal radiated by the source antenna.

[0009] According to a second aspect of the present invention, there is provided a non-transitory computer program product comprising instructions for implementing the steps of the method according to any one of the preceding claims when loaded and run on a computing device of a computing apparatus.

[0010] According to a third aspect of the present invention, there is provided a sampling device for sampling an electromagnetic field according to claim 12.

[0011] According to a fourth aspect of the present invention, there is provided a system for locating and characterizing one or more electromagnetic radiation sources according to claim 16.

[0012] Other aspects of the present invention are recited in the appended dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] With reference to the accompanying drawings, other features and advantages of the present invention will become apparent from the following description of non-limiting exemplary embodiments, in which:

[0014] Figure 1 A measuring device or system for locating and characterizing electromagnetic radiation sources is shown;

[0015] Figure 2 A measuring device that can be used to sample the electromagnetic field generated by an electromagnetic radiation source is shown;

[0016] Figure 3 The echo loss measured for an exemplary half-wave dipole antenna to be located is shown;

[0017] Figure 4 The time-reversed version of the measured electrical signal of the dipole antenna to be located is shown;

[0018] Figure 5 Is shown once with Figure 4The time-reversed version of the measured signal excites the simulation model, the normalized maximum of E in the observation plane over all time samples; y ;

[0019] Figure 6 Shows that in the scenario of Figure 5 at y = E y,max , the normalized maximum of E over all time samples along the X-axis; y ;

[0020] Figure 7 Shows that once the simulation model is excited by the time-reversed version of the measured signal shown in Figure 4 , the normalized maximum of E in the observation plane over all time samples, but where the antenna to be located has been rotated by 90° compared to the case of x ; Figure 5 ;

[0021] Figure 8 Shows the comparison between the normalized excitation signal of the dipole antenna and the normalized reconstructed waveform;

[0022] Figure 9 Shows the echo loss measured for the example patch antenna to be located and the structure of the patch antenna;

[0023] Figure 10a And Figure 10b Show respectively the distribution of the normalized maximum E Figure 9 component in the X-Y plane of the observation plane 5 mm of the patch antenna towards the sampling device and the distribution of the normalized maximum reconstructed E x in the observation plane; x ;

[0024] Figure 10c And Figure 10d Show respectively the distribution of the normalized maximum E Figure 9 component in the X-Y plane of the observation plane 5 mm of the patch antenna towards the sampling device and the distribution of the normalized maximum reconstructed E y in the observation plane; y ;

[0025] Figure 11 Shows the comparison of the direct calculation and the reconstructed calculation of the directivity of the electric and magnetic fields of the Figure 9 patch antenna at 21.5 GHz;

[0026] Figure 12a And Figure 12b Provide respectively the direct calculation of the 3D normalized total radiation power of the Figure 9 patch antenna and the reconstructed calculation at 21.5 GHz; and

[0027] Figure 13a and Figure 13b is a flow chart showing the steps of a proposed method for locating and characterizing one or more electromagnetic radiation sources. Detailed Description of the Invention

[0028] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Identical or corresponding functional and structural elements that appear in different drawings have the same reference numerals.

[0029] Figure 1 shows a measuring device or arrangement for measuring the electromagnetic field generated by an electromagnetic radiation source (e.g., an antenna). The sampling device 1 is configured to spatially sample the electromagnetic field generated by the radiation source 3, which is placed at a distance Z from the front face 5 of the sampling device 1. 0 at. In Figure 2 a sampling device without the front face 5 is better shown, which includes a resonant cavity structure.

[0030] The dimensions of the cavity are advantageously selected such that the first resonant frequency of the cavity is higher than the frequency range of the source (i.e., the frequency range of the signal radiated by the source). This means that the length of each dimension of the cavity (in this case length, height, and width) is at least equal to the wavelength of the electromagnetic radiation emitted by the source. The front face or surface 5 facing the source 3 in operation includes an array of holes or perforations. The sampling device (especially the front face) may alternatively or additionally include an electromagnetic metasurface. The metasurface can be any structure with a uniform or non-uniform pattern of sub-wavelength size. This metasurface has the property of generating an electric field with low spatial autocorrelation in the observation plane. In this example, the holes 7 or perforations, which are through-holes, are arranged in a periodic array with a given spatial separation between any two adjacent holes. In this example, as Figure 2 shown, circles 15 are provided at one or more interior corners of the cavity 9, which are optional features. The circles can be, for example, spherical or elliptical. However, any other shape can be used, e.g., an elongated rod, and the shape(s) can be placed anywhere within the cavity. One or more shapes 15 serve as one or more mode mixing features or structures 15 provided within the cavity to enhance the mixing mode characteristics of the cavity. In this example, the observation plane 11 or more generally the observation region is considered to be at a far-field distance from the cavity in the X-Y plane defined by the front face 5 (but this is not necessary). The L z dimension is the thickness of the sampling device. One or more sources to be detected and / or characterized are placed in the observation plane 11 or within the observation region (a three-dimensional volume can be defined). The electromagnetic field emitted from the source will reach the front face 5 of the cavity at Z = 0.

[0031] Also as Figure 2As shown, the sampling device thus includes a solid object or body having a cavity therein and providing one or more sensors 13 or probes within the cavity. In this example, the body forms a substantially enclosed body (i.e., a body enclosed on all sides) with a perforated front face. In this case, the sampling device is made of a metallic element, but the sampling device can also be made of any conductive material. Additionally, when disregarding the shape 15, the cavity has a rectangular shape in this example, but other cavity shapes are possible. As will become clear later, the cavity 9 can be considered a time-reversal mirror. In the time-reversal method, reflections from the cavity surface can simulate an infinite number of sensors. By using only one sensor, the focusing properties of the time-reversal cavity can be utilized to locate an electromagnetic source.

[0032] Except for the position of the holes 7, the boundary conditions are imposed on the front face of the cavity represents the electric field component tangent to the X - Y plane when Z≥0, while represents the electric field component tangent to the X - Y plane when Z<0. At the positions of these holes, can be written more thoroughly, where:

[0033]

[0034] Since J x = J y = 0

[0035]

[0036] In the above equations, the superscript "1" refers to the case of Z≥0, the superscript "2" refers to the case of Z<0, E represents the electric field, H represents the magnetic field, J represents the current density, x represents the component along the X - axis, y represents the component along the Y - axis, and z represents the component along the Z - axis.

[0037] According to Bethe's diffraction theory for small holes, H.A. Bethe, "Theory of diffraction by small holes", Phys. Rev., Vol. 66, Nos. 7 - 8, pp. 163 - 182, October 1944, the diameter of the holes should be small compared to the wavelength being measured. Thus, it can be assumed that the magnetic field does not vary within any given hole. On the other hand, the size of the holes cannot be too small as this would result in only a small amount of electromagnetic field coupling to the inside of the cavity. In the specific example explained below, the hole diameter is considered to be approximately λ min / 2, where λ min represents the minimum wavelength of the electromagnetic radiation emitted by the source 3. It should be noted that the hole diameter is preferably from λ min / 5 to λ minin the range of λ / 2 or more specifically λ min from λ / 4 to λ min values taken within the range of λ / 2. It should be noted that the cross-section of the hole does not have to be circular, but any other cross-sectional hole shape in the X-Y plane is possible. Therefore, the diameter can be understood as the maximum cross-sectional dimension of the hole.

[0038] As Figure 1 shown, an array of holes is thus arranged on the front wall of the cavity. This array of holes can be understood in the form of a spatial field sampler, which can be used to replace the deployment of multiple arrays of field sensors or to replace the use of a rasterized scanner.

[0039] This problem can be imagined in the frequency domain. In this example, the front face 5 of the cavity 9 is in the far-field region of the source 3, and a plane-wave approximation of the field distribution at Z = 0 can be considered. In this case, the lateral dimension of the cavity (in the X-Y plane) is greater than several λ min . Therefore, sufficient spatial sampling points are required to ensure the spatial Nyquist rate. In addition, in this example, the spatial sampling period, i.e., the spatial interval between any two adjacent holes, is set to λ min / 2.

[0040] Once the magnetic field is sampled by the front face of the cavity, the electromagnetic uniqueness theorem can be considered and a magnetic current source can be obtained at the position of the hole 7 on the inner surface of the cavity 9. The electromagnetic uniqueness theorem states that providing boundary conditions for Maxwell's equations uniquely fixes the solutions of these equations. Since Maxwell's equations fully describe all electromagnetic interactions, Maxwell's equations also apply to the presence of electromagnetic sources. There are two main types of electromagnetic sources, namely electric sources and magnetic sources. In Maxwell's equations, electric sources are represented by a current density with units of A / m 2 and magnetic sources are a magnetic flux density with units of T. In addition, the strong mode mixing characteristics of chaotic microwave cavities are an established fact. Considering only the propagation of plane-wave fields in chaotic cavities, the field at each position inside the cavity can be regarded as a superposition of many rays with different phases and directions.

[0041] Each magnetic current source at each hole location generates rays in all directions within the cavity and excites the chaotic and bouncing ball modes of the cavity (see K. Selemani, J. B. Gros, E. Richalot, O. Legrand, O. Picon, and F. Mortessagne, "Comparison of reverberation chamber shapes inspired from chaotic cavities", IEEE Trans. Electromagn. Compat., Vol. 57, No. 1, pp. 3 - 11, February 2015, for the definition of these modes). The fields inside the cavity are measured by one or more sensors 13, and these rays will reach our measurement points (i.e., the sensor locations) via many paths and contribute to the total recorded field or signal at the measurement points. In other words, the fields sampled by the holes 7 in the front face 5 of the cavity 9 are strongly coupled to the modes of the cavity.

[0042] In the next step, the proposed method uses time - reversal processing to decode the information in the electrical signals measured or recorded at the measurement points. In other words, time - reversal processing is used to decode the information hidden in the fields inside the cavity. In time - reversal processing, the original source 3 to be detected and characterized is removed from the solution space, and the signal is time - reversed and injected into an electromagnetic field solver, which is a computer simulation model. The solver models the sampling device and is configured to solve Maxwell's equations. For example, an example of such a solver is given in the publication by Oskooi, Ardavan F. et al., "MEEP: A flexible free - software package for electromagnetic simulations by the FDTD method", Computer Physics Communications 181.3 (2010): 687 - 702. The solver is calibrated at least with the dimensions and geometry of the sampling device 1, in particular the dimensions and geometry of the cavity 9. By observing the field components in the observation plane 11, the source 3 can be located and characterized.

[0043] Time reversal or T-symmetry describes the symmetry of physical laws under time-reversal transformation: t → -t. The time-reversal operation causes the original signal to flip with respect to its amplitude axis (i.e., usually the reference vertical axis). This indicates that the operation causes the signal to be reflected along its reference amplitude axis (i.e., usually the reference vertical axis). This operation is called time reversal or time reflection of the signal. In the past few decades, this technique has many applications in the engineering field, especially in source location identification, such as mine detection and fault location in power grids.

[0044] The time-reversal operation in signal processing can be understood as a spatial focusing technique using the reciprocity principle. One can imagine a signal emitted from the transmission location, which in the present invention is the antenna to be located and characterized. The signal can be picked up at several receiving locations (i.e., sensor locations). The sensors also record these received signals. Now, the system can be looked at in reverse. The previous receiving locations can become the transmission locations. These locations (when transposed into the simulation model, as described below) simultaneously transmit the previously recorded signals in a time-reversed manner. At the target location in the model (corresponding to the original transmitter or antenna in the current case), all the signals converge or focus in space (i.e., the convergence location in the model).

[0045] An exemplary numerical model is explained below. In this study, forward propagation and backward propagation were carried out using a transient electromagnetic field solver. The solver uses the finite integration technique (FIT) to solve the integral form of Maxwell's equations. It should be noted that in an actual scenario, forward propagation will be analyzed via measurement, and backward propagation will be analyzed through numerical simulation using the solver.

[0046] First, the details of the implemented structure are given. Thereafter, case studies of source location, surface current reconstruction, and far-field pattern reconstruction using the proposed concept are shown. The implemented geometry is as Figure 1 and Figure 2 shown. The diameter of the holes is 5 mm. The number of holes along the X-axis and Y-axis is 17 (i.e., a total of 17×17 holes), and they are placed at a period of 10 mm apart from each other. The size of the cavity itself is 200 mm×200 mm×53 mm. The radius of the sphere is 45 mm. The observation plane is located at Z = 60 mm, which is farther than the far-field limit of 2D 2 / λ, where D represents the maximum size of the source. The length of the receiving probe antenna is 6.4 mm and is located at -50 mm, -50 mm, -26.5 mm from the center of the front face of the cavity 9 by 5.

[0047] Source localization

[0048] As a first example, a half-wave dipole antenna is considered as the radiator to be localized. The length of the antenna in this example is 6.4 mm. The dipole antenna return loss measured at the input of the source antenna is as Figure 3 shown. The dipole antenna is placed on the observation plane at x = 50 mm, y = 50 mm, extending along the Y-axis. The dipole antenna is excited with a Gaussian waveform having a bandwidth from 17.5 to 26.5 GHz. The signal emitted by the dipole is recorded with our probe antenna, which is located at x = -50 mm, y = -50 mm, z = -26.5 mm, extending along the Y-axis. The time-reversed version of the recorded signal is as Figure 4 shown.

[0049] In the next step, the source is removed from the observation plane and the electromagnetic field solver is excited with the time-reversed version of the recorded signal as Figure 4 shown. Figure 5 Shows the maximum value of E y in the observation plane over all time samples. We can see that the magnetic field refocuses at the main position of the source. The cross indicates the main position of the source. Taking the center of the antenna as the antenna position, the positioning error is 1.5 mm.

[0050] Figure 6 Shows the resolution of the diffraction-limited focus. The achieved resolution (i.e., the minimum separation between sources that allows them to be distinguished from each other) is approximately 12 mm. It should be noted that a resolution better than λ min / 2 can be achieved by reducing the size of the aperture. However, in a practical scenario, the limited SNR of the sampling device may limit the performance of the positioning.

[0051] In this paper, to ensure that the proposed method is applicable to other polarizations, the same source antenna is considered, but it is rotated to be along the X-axis. It should be noted that, similar to the first case above, our probe antenna 3 is oriented along the Y-axis. Figure 7 Shows the distribution of the normalized maximum value of E x in the observation plane. In this case, the positioning error is 2.6 mm. This result shows the effective conversion of the polarization of the mode mixing cavity.

[0052] Surface current reconstruction

[0053] It has been seen that using the proposed system, an electromagnetic radiation source can be localized. Figure 8 Compares the normalized excitation signal of the source and the normalized reconstructed waveform (the field back-propagated at the source position). It can be observed that the waveform can be recovered with a fairly good accuracy.

[0054] So far, it has been shown that the proposed method can recover the field waveform at the position of source 3. We now compare the field distributions on the surface near the source.

[0055] An X - polarized patch or microstrip antenna (i.e., source 3) with patch dimensions of 6.4 mm (along the X - axis) and 4.2 mm (along the Y - axis) is placed 60 mm in front of the cavity 9 along the Z - axis. The patch antenna and its return loss are as Figure 9 shown.

[0056] Compare the distribution of the normalized maximum electric field in the X - Y plane at a distance of 5 mm from the sampling device towards the observation plane and the distribution of the estimated or reconstructed normalized maximum electric field in the observation plane (Z = 60 mm). Figure 10a and 10b show the results of the E x field, while Figure 10c and Figure 10d show the results of the E y field. It can be seen that a fair agreement can be obtained for the field distribution. The main difference between these two case studies is that for the actual field, the near - field components still exist, while in the reconstructed field distribution, the evanescent field components (one component is a near - field component and the other is a radiation - field component) do not exist, because the sensor 3 and the cavity 9 are placed in the far - field of the patch antenna.

[0057] Far-field antenna pattern reconstruction

[0058] Next, the reconstructed field is used, and the near - field to far - field transformation is used to derive the antenna directivity. In this example, the patch antenna is placed in the far - field of the cavity (Z = 60 mm). To this end, the reconstructed electric field at Z = 60 mm is recorded. The fast Fourier transform is applied to derive the field distribution at the frequencies of interest, and the near - field to far - field transformation is used to calculate the field distribution in the far - field to obtain the directivity pattern of antenna 3. Figure 11 shows the comparison of the directivity calculated directly and reconstructed at 21.5 GHz, while Figure 12a and Figure 12b provide this comparison of the 3D normalized total radiated power, where Figure 12a shows the reference pattern, while Figure 12b shows the reconstructed pattern.

[0059] Figure 13a and 13bThe flowchart outlines the steps of the proposed source localization and characterization process. In step 101, one or more sources 3 (i.e., antennas in this case) are placed in front of the sampling device 1 in the observation plane, at a predetermined distance from the front face 5 of the sampling device. In step 103, one or more sensors 13 within the cavity 9 measure one or more electrical signals (in this example, the amplitudes of these signals are given as voltages). Thus, these signals can be considered (digital) electrical activity signals. It should be noted that each sensor measures one electrical signal. Therefore, the electrical signals measured by different sensors may vary slightly from each other. In this step, thus, one or more electrical signals are collected. In step 105, an electromagnetic field solver for modeling the sampling device is obtained. This step may also include calibrating the electromagnetic field solver at least with the dimensions and geometry of the sampling device 1. In step 107, the measured or collected electrical signals are time-reversed, and in step 109, the time-reversed electrical signals are input into the electromagnetic field solver at the simulated input positions. The method may optionally include performing a signal filtering operation on one or more of the collected electrical signals and / or one or more of the time-reversed electrical signals before inputting the one or more time-reversed electrical signals into the electromagnetic field solver to improve the signal quality. It should be noted that one or more sensors are each located at a corresponding sensing position such that the one or more sensing positions can be understood to have a first spatial relationship with respect to each other (e.g., the distance between sensors). One or more time-reversed electrical signals can be arranged to be input into the electromagnetic field solver at corresponding input positions such that the one or more input positions can be understood to have a second spatial relationship with respect to each other, and wherein the first spatial relationship can be the same or substantially the same as the second spatial relationship. Thus, the time-reversed electrical signals 21 can be configured to be fed into the solver at different positions.

[0060] In step 111, the electromagnetic field solver reconstructs the electromagnetic field at least at a simulated or modeled observation plane corresponding to the (spatially) observation plane 11. For this purpose, a time-reversed electrical signal is used as the input signal for the electromagnetic field solver. In step 113, the electromagnetic field solver locates one or more modeled or simulated sources in the simulated observation plane or the simulated observation region. Each modeled source has its corresponding original source 3. The location of one or more sources can be achieved by finding the focus in the simulated observation plane. The distribution of the maximum field can be used to achieve this. In other words, the focus can be identified by using a given identification criterion, where the identification criterion is a threshold of the reconstructed electromagnetic field. In step 115, the reconstructed electromagnetic field is optionally time-reversed in the simulated observation plane. In step 117, the surface current distribution is reconstructed for the simulated sources using the time-reversed reconstructed electromagnetic field (or, if the time-reversed version of the field is not available, the non-time-reversed reconstructed electromagnetic field). In step 119, the reconstructed (far-field) radiation pattern is calculated or determined for one or more modeled sources using the reconstructed surface current distribution or the near-field to far-field transformation of the time-reversed reconstructed electromagnetic field (or, if the time-reversed version of the field is not available, the non-time-reversed reconstructed electromagnetic field). It should be noted that the reconstructed field in the observation plane can be regarded as the near-field radiation component of the located source. Using the well-known plane wave spectrum (PWS) method, for example, the method explained in "Antenna theory: analysis and design", Volume 1, C.A. Balanis, John Wiley & Sons, 2005, the far-field distribution of the located source can then be calculated. The reconstructed surface current distribution technique is based on the surface equivalence principle, for example, as explained in "Time-Harmonic Electromagnetic Fields", Roger F. Harrington, McGraw-Hill, Inc., 1961. In this article, we can define a fictitious surface around the located source S . By knowing the reconstructed electric and magnetic fields in the observation plane and forcing S the electric and magnetic fields inside to be zero, the surface equivalent current can be obtained as follows:

[0061]

[0062] where represents the current density, is the normal to the surface S, represents the magnetic field, represents the electric field, Denotes the magnetic flux density. By deriving the well-known electric field integral equation, the electric and magnetic fields in the far-field region can be obtained. Accordingly, the corresponding reconstructed far-field radiation patterns of one or more modeled sources are obtained directly or indirectly from the reconstructed electromagnetic fields.

[0063] As described above, the present invention proposes a novel hardware device or system and a single-space sampling method for localizing and characterizing electromagnetic sources (wherein the electrical signals can be measured only once). The characterization includes deriving the antenna radiation pattern based on the space sampling scheme. The hybrid-mode characteristics of the cavity are used to encode the information of the sampled electric field. As a proof of concept, the results of source localization, surface current reconstruction, and far-field pattern reconstruction are given. The proposed method can be used as a fast and cost-effective solution for antenna pattern measurement and electromagnetic compatibility (EMC) testing.

[0064] Some of the method steps in the above method steps can be performed by a suitable circuit or circuitry. The terms "circuit" and "circuitry" refer to physical electronic components or modules (e.g., hardware) and any software and / or firmware ("code") that can configure the hardware, be executed by the hardware, and / or otherwise be associated with the hardware. Thus, a circuit can be configured or operable to perform, or include means for performing, the required methods as described above.

[0065] Although the present invention has been described in detail in the drawings and the foregoing description, such description and illustration are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Based on the study of the drawings, the disclosure, and the appended claims, other embodiments and variations can be understood and effected by those skilled in the art in practicing the claimed invention. For example, all or part of the calculations (i.e., data processing) taught by the present invention can be implemented as cloud computing by using computing capabilities on the Internet.

[0066] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

1. A method for locating and characterizing one or more electromagnetic radiation sources (3), the method comprising the steps of: collecting (103) one or more electrical signals received from the one or more sources (3) in an observation region (11) placed in front of a sampling device (1), the sampling device being configured to measure the one or more electrical signals; performing time reversal (107) on the collected one or more electrical signals; inputting (109) the one or more time-reversed electrical signals into an electromagnetic field solver that models the sampling device (1) and is configured to solve Maxwell's equations; determining (111) a reconstructed electromagnetic field by running the electromagnetic field solver with the one or more time-reversed electrical signals as one or more input signals; identifying (113) one or more foci in the reconstructed electromagnetic field so as to locate one or more modeled sources in a simulated observation region; obtaining (119) a corresponding reconstructed far-field radiation pattern of the one or more modeled sources directly or indirectly from the reconstructed electromagnetic field.

2. The method according to claim 1, wherein, the one or more time-reversed electrical signals converge at one or more convergence positions when input into the electromagnetic field solver, and wherein identifying the one or more foci includes detecting the one or more convergence positions.

3. The method according to claim 1 or 2, wherein, the method further comprises placing (101) the one or more sources (3) in front of the sampling device (1) in the observation region (11).

4. The method according to any one of the preceding claims, wherein, the one or more foci are identified by using a given identification criterion, wherein the identification criterion is a threshold of the reconstructed electromagnetic field.

5. The method according to any one of the preceding claims, wherein, the corresponding reconstructed far-field radiation pattern is obtained by using a near-field to far-field transformation process with the reconstructed electromagnetic field.

6. The method according to any one of claims 1 to 4, wherein, the corresponding reconstructed far-field radiation pattern is obtained by reconstructing a corresponding surface current distribution of the one or more modeled sources from the reconstructed electromagnetic field or from a time-reversed reconstructed electromagnetic field, and by using the corresponding reconstructed surface current distribution to obtain the corresponding reconstructed far-field radiation pattern.

7. The method according to any one of the preceding claims, wherein, the method further comprises calibrating the electromagnetic field solver at least by using the size and geometry of the sampling device (1).

8. The method according to any one of the preceding claims, wherein, the sampling device (1) comprises a body having a cavity (9) therein, wherein the body comprises a perforated front wall (5) having a set of holes (7) and / or a metasurface and facing the one or more sources (3), and wherein one or more sensors (13) are placed in the cavity (9) for measuring the one or more electrical signals.

9. The method according to any one of the preceding claims, wherein, the observation region (11) forms an observation plane (11), and the simulated observation region forms a simulated observation plane.

10. The method according to any one of the preceding claims, wherein, the method further comprises performing a signal filtering operation on the one or more collected electrical signals and / or the one or more time-reversed electrical signals before inputting the one or more time-reversed electrical signals into the electromagnetic field solver.

11. A non-transitory computer program product comprising instructions for implementing the steps of the method according to any one of the preceding claims when loaded and run on a computing device of a computing apparatus.

12. A sampling device (1) for sampling an electromagnetic field generated by one or more electromagnetic radiation sources (3) placed in front of the sampling device (1), the sampling device comprising a substantially enclosed body made of a conductive material, and a cavity (9) formed within the substantially enclosed body, the substantially enclosed body comprising a perforated front face (5), the perforated front face comprising a set of holes (7) and / or a sub-surface forming a spatial field sampler of the electromagnetic field, and facing the one or more sources (3), wherein, one or more sensors (13) are located in the cavity (9) for measuring one or more electrical signals.

13. The sampling device according to claim 12, wherein, The diameter of the hole is in the range of λ min / 5 and λ min / 2, where λ min represents the minimum wavelength of the electromagnetic signal generated by the one or more sources (3).

14. The sampling device according to claim 12 or 13, wherein, the set of holes (7) forms a periodic array of holes, and / or wherein the cavity (9) comprises one or more mode mixing structures (15) to enhance the hybrid mode characteristics of the cavity (9), and / or wherein the dimensions of the cavity (9) are such that a first resonance frequency of the cavity (9) is higher than a frequency range of the one or more sources.

15. The sampling device according to any one of claims 12 to 14, wherein, the first resonance frequency of the cavity is higher than the frequency range of the one or more electromagnetic radiation sources (3).

16. A system for locating and characterizing one or more electromagnetic radiation sources (3), the system comprising means for: collecting one or more electrical signals received from the one or more sources (3) in an observation region (11) placed in front of a sampling device (1), the sampling device being configured to measure the one or more electrical signals; time-reversing the one or more collected electrical signals; inputting the one or more time-reversed electrical signals into an electromagnetic field solver that models the sampling device (1) and is configured to solve Maxwell's equations; determining a reconstructed electromagnetic field by running the electromagnetic field solver with the one or more time-reversed electrical signals as one or more input signals; identifying one or more focal points in the reconstructed electromagnetic field so as to locate one or more modeled sources in a simulated observation region; The corresponding reconstructed far-field radiation patterns of the one or more modeled sources are obtained directly or indirectly from the reconstructed electromagnetic field.

Images