Aerial measurement system and method

Abstract

An over-the-air OTA measurement system (10) for testing a reconfigurable intelligent surface (RIS) is described. The OTA measurement system (10) includes at least one signal generator module (18) configured to generate at least one RF signal. The OTA measurement system (10) also includes at least one RF antenna (28) configured to transmit at least one RF signal. The OTA measurement system (10) also includes a locator unit (26) configured to hold the RIS module (16) in an adjustable position, where the locator unit is configured to modify the adjustable position. The at least one RF antenna (28) is further configured to receive the at least one reflected RF signal. The OTA measurement system (10) is configured such that a far field condition of the at least one transmitted RF signal is provided at the RIS module (16) and a far field condition of the at least one reflected RF signal is provided at the at least one RF antenna (28). In addition, an OTA measurement method is described.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to an over-the-air measurement system for testing a reconfigurable intelligent surface. The present invention also relates to an over-the-air measurement method for performing over-the-air measurements by means of the OTA measurement system. BACKGROUND

[0002] A reconfigurable intelligent surface (RIS) reflects an incident RF signal into a certain configurable direction, thereby allowing to shape the propagation path of the RF signal. In other words, a RIS allows for passive beamforming of RF signals.

[0003] A RIS can be used to extend the range of wireless communication devices, as well as to improve the quality of data links between wireless communication devices by appropriately adjusting the lobes of RF signals to the location of the respective wireless devices.

[0004] In fact, RISs can be a key technology for upcoming wireless communication standards such as 6G.

[0005] As with other devices employed in wireless communication, RISs need to be tested with respect to their operational properties, such as the beamforming capabilities of a RIS.

[0006] For example, a RIS is tested by means of a dual-base antenna over-the-air (OTA) measurement system, which comprises a feed antenna that transmits RF signals to the RIS and a probe antenna that receives reflected RF signals from the RIS. SUMMARY

[0007] It is an object of the present invention to provide an OTA measurement system and an OTA measurement method that are more efficient in terms of manufacturing costs and / or space requirements.

[0008] According to the present invention, the problem is solved by an over-the-air (OTA) measurement system for testing a reconfigurable intelligent surface (RIS). The OTA measurement system comprises at least one signal generator module, wherein the at least one signal generator module is configured to generate at least one radio frequency (RF) signal. The OTA measurement system further comprises at least one RF antenna, wherein the at least one RF antenna is connected to the at least one signal generator module to receive the at least one RF signal, and wherein the at least one RF antenna is configured to emit the at least one RF signal. The OTA measurement system further comprises a positioner unit configured to hold a RIS module in an adjustable position, wherein the positioner unit is configured to modify the adjustable position. The at least one RF antenna is further configured to receive at least one reflected RF signal, wherein the at least one reflected RF signal corresponds to the at least one RF signal reflected by the RIS module. The at least one RF antenna comprises only one RF antenna or only one RF antenna array which is used as both transmitter and receiver for the at least one RF signal. The OTA measurement system is configured such that far-field conditions for the at least one emitted RF signal are provided at the RIS module and far-field conditions for the at least one reflected RF signal are provided at the at least one RF antenna. The OTA measurement system further comprises at least one receiver module connected to the at least one RF antenna in order to receive the at least one reflected RF signal from the at least one RF antenna. The OTA measurement system further comprises a signal processing module, wherein the signal processing module is configured to determine at least one reflection parameter based on the at least one RF signal and the at least one reflected RF signal.

[0009] In the following and hereinbefore, the term “module” is understood to describe a suitable hardware, a suitable software or a combination of hardware and software configured to have a specific functionality.

[0010] The hardware can especially comprise a CPU, a GPU, a FPGA, an ASIC or other types of electronic circuits.

[0011] Furthermore, especially in the case of a RIS module, the hardware can comprise reconfigurable capacitors, inductors and / or resistors.

[0012] The RIS module can comprise or be connected to a RIS controller configured to adjust the capacitance, the inductance and / or the resistance of the individual cell of the RIS module, thereby modifying the reflectivity properties of the RIS module.

[0013] The term “position” is understood to denote a position, e.g. x, y and z coordinates, and an orientation, e.g. expressed in Euler angles.

[0014] The present invention is based on the finding that a single RF antenna or a single antenna array which is used as both transmitter and receiver for the RF signal is sufficient to test a RIS module.

[0015] Based on the at least one reflection parameter determined via the measurement by the single RF antenna or the single RF antenna array, a correlation quality factor of the RIS module can be determined in a post-processing based on the at least one reflection parameter.

[0016] In other words, the OTA measurement system according to the present application allows testing of a RIS using a single RF antenna or a single RF antenna array which is used as both a transmitter antenna and a receiver antenna at the same time, instead of employing at least one dedicated transmitter antenna and at least one dedicated receiver antenna.

[0017] Thus, compared to the prior art, the number of RF antennas required for testing the RIS module is halved, thereby greatly reducing the manufacturing costs of the OTA measurement system.

[0018] Furthermore, the spatial requirements of the OTA measurement system are also reduced, since the far-field conditions only have to be provided between one RF antenna (antenna array) and the RIS module, instead of between two antennas (antenna arrays) arranged on opposite sides of the RIS module.

[0019] Generally, the at least one reflection parameter relates to electrical signals supplied to and received from the at least one RF antenna.

[0020] The determined at least one reflection parameter can be or comprise at least one S-parameter or any other suitable type of reflection parameter.

[0021] In particular embodiments, the determined at least one reflection parameter can comprise a parameter with an amplitude of S11, in particular measured with a vertical polarization of the RF signal, and a parameter with an amplitude of S22, in particular measured with a horizontal polarization of the RF signal.

[0022] The positioner unit can be configured to modify the adjustable position such that far-field conditions at the at least one RF antenna and at the RIS module are preserved.

[0023] According to the present application, the at least one RF antenna comprises only one RF antenna or only one RF antenna array. As already explained above, for the OTA measurement system according to the present disclosure, a single RF antenna or a single RF antenna array has been sufficient, thereby reducing the manufacturing costs and spatial requirements of the OTA measurement system compared to multi-antenna OTA measurement systems.

[0024] According to one aspect of the present application, the positioner unit is configured to adjust an azimuth angle, an elevation angle and / or a height of the RIS module. By adjusting the azimuth angle and / or the elevation angle, different relative orientations of the RIS module and the at least one antenna can be tested. By adjusting the height, different portions of the RIS module can be tested.

[0025] Thus, the positioner unit can adjust one, two or three degrees of freedom of the RIS module position.

[0026] However, it is also conceivable that the positioner unit can be configured to adjust all degrees of freedom of the RIS module position or any subset of the degrees of freedom of the RIS module position.

[0027] As already mentioned above, the positioner unit can modify the azimuth angle, the elevation angle and / or the height such that far-field conditions at the at least one RF antenna and at the RIS module are preserved.

[0028] In one embodiment of the application, the signal processing module is configured to determine an OTA reflection parameter of the RIS module based on the at least one reflection parameter. Generally, the OTA reflection parameter describes the reflectivity properties of the RIS module, i.e. the properties of the at least one reflected RF signal depend on the at least one transmitted RF signal.

[0029] The at least one reflection parameter and thus the OTA reflection parameter can include a contribution from reflections in the OTA measurement system other than the desired reflection to be measured, which is the reflection of the at least one RF signal from the RIS module back to the at least one RF antenna.

[0030] The signal processing module is configured to extract this desired contribution based on the determined at least one reflection parameter.

[0031] In fact, the signal processing module can be configured to apply a time-gating algorithm to determine the OTA reflection parameter, in particular wherein the signal processing module is configured to apply the time-gating algorithm to the reflected RF signal to determine the OTA reflection parameter.

[0032] As mentioned above, the at least one reflection parameter includes a contribution from other reflections in the OTA measurement system. By applying a suitable time-gating, the desired reflection signal can be isolated to determine the at least one reflection parameter such that the other reflections do not impair the measurement result of the at least one reflection parameter.

[0033] For example, a window function such as a Hann window can be applied to the reflected RF signal to determine the at least one reflection parameter and thus the OTA reflection parameter.

[0034] As another example, at least one background reflection parameter can be determined without the RIS module in the positioner unit and can be subtracted from the at least one reflection parameter determined from the RIS module placed in the positioner unit, thereby compensating for unwanted reflections.

[0035] In another embodiment of the present invention, the positioner unit is configured to continuously modify the adjustable position to a set of different positions, and the signal processing module is configured to separately determine the OTA reflection parameter at each of the different positions (in particular, at each of the different positions). Thus, the OTA reflection parameter, and thus the reflectivity property of the RIS module, can be determined for a plurality of different relative positions (in particular, for a plurality of different relative orientations) of the at least one RF antenna and the RIS module. In fact, the angular distribution of the OTA reflection parameter, and thus the angular distribution of the reflectivity property, can be determined.

[0036] The number of different positions at which the above measurements are performed determines the resolution of the determined OTA reflection parameters.

[0037] The number of different positions may be adjustable, in particular by a user of the OTA measurement system. Thus, the resolution may be adjustable.

[0038] One aspect of the present invention provides that a signal processing module is configured to determine a monostatic OTA reflection pattern of a RIS module based on OTA reflection parameters determined at different locations. Generally, the monostatic reflection pattern describes the reflectivity properties of an RF signal received from a source and returned to the source by the RIS module for a plurality of different relative positions of the RIS module to the source (particularly, at a plurality of different relative orientations).

[0039] In one embodiment of the present invention, the signal processing module is configured to determine a bistatic OTA reflection pattern for the RIS module based on the determined monostatic OTA reflection pattern (particularly by applying Falconer's monostatic to bistatic equivalence theorem or a generalized monostatic to bistatic equivalence theorem to the determined monostatic OTA reflection pattern). In other words, by appropriately transforming the determined monostatic OTA reflection pattern, a bistatic OTA reflection pattern (which corresponds to an OTA reflection pattern measured using at least one dedicated transmit antenna and at least one dedicated receiver antenna) can be determined in post-processing based on the monostatic OTA reflection pattern obtained using a single RF antenna or a single RF antenna array. Consequently, there is no need to provide more than one RF antenna or more than one RF antenna array to determine the bistatic OTA reflection pattern, thereby reducing the manufacturing cost and space requirements of the OTA measurement system.

[0040] In another embodiment of the present invention, the OTA measurement system further includes a measuring instrument, wherein the measuring instrument includes at least one signal generator module, at least one receiver module, and / or a signal processing module, and in particular, wherein the measuring instrument is a network analyzer, a vector network analyzer, or a spectrum analyzer. However, it should be understood that the measuring instrument can be configured as any other suitable type of measuring instrument, in particular, any other type of amplitude measuring instrument.

[0041] The at least one reflection parameter may comprise phase information about the at least one RF signal and / or the at least one reflected RF signal. However, this is not mandatory.

[0042] In fact, the at least one reflection parameter may be an amplitude, ie the at least one reflection parameter may describe the amplitude of the RF signal in dependence on the at least one reflection of the at least one transmitted RF signal.

[0043] The at least one RF signal generated by the at least one signal generator module can be a continuous wave (CW) signal or a modulated signal. The frequency of the CW signal or the frequency of the carrier signal of the modulated signal can correspond to the operating frequency of the RIS module. Therefore, the RIS module can be tested using the frequency of the at least one RF signal corresponding to the operating frequency of the RIS module.

[0044] Herein and hereinafter, the term "operating frequency of a RIS module" is understood to mean the center frequency at which the corresponding RIS module is configured. Typically, a RIS has a rather narrow operating frequency bandwidth around the operating frequency.

[0045] The frequency of the generated at least one RF signal may be equal to an operating frequency of the RIS module, or may be within a frequency bandwidth around the operating frequency.

[0046] For example, the frequency of the CW signal or the frequency of the carrier signal may be between 1 GHz and 10 THz.

[0047] However, it should be understood that the RIS module can have any operating frequency, ie also below 1 GHz or above 10 GHz. Therefore, the frequency of the CW signal or the frequency of the carrier signal can be below 1 GHz or above 10 THz.

[0048] In one embodiment of the present invention, the at least one RF antenna includes only one RF antenna array, wherein the RF antenna array is configured as a plane wave converter, and wherein the adjustable position is located in a quiet zone of the RF antenna array. Thus, the far-field condition of the at least one RF signal at the RIS module and the far-field condition of the at least one reflected RF signal at the RF antenna array can be synthesized by the RF antenna array configured as a plane wave converter. This allows the RIS module to be placed in an area that is typically the near-field region of the at least one RF antenna, thereby further reducing the space requirements of the OTA measurement system according to the present disclosure.

[0049] From this point on and in the following, the term "quiet zone" is understood to mean a spatial region or zone where at least one RF signal emitted by an RF antenna array has defined properties. In this example, the quiet zone refers to a region where far-field conditions are reliably synthesized by the RF antenna array.

[0050] One aspect of the present invention provides an OTA measurement system, further comprising at least one reflector, wherein the at least one reflector is arranged and configured such that the at least one RF signal transmitted by the at least one RF antenna is forwarded to the RIS module, wherein the at least one reflector is arranged and configured such that the at least one reflected RF signal is forwarded to the at least one RF antenna, and wherein the at least one RF antenna, the at least one reflector and the adjustable position are arranged such that far-field conditions are provided at the RIS module and at the at least one RF antenna. Thus, far-field conditions can be obtained by the at least one reflector, which effectively increases the distance between the at least one antenna and the RIS module. This allows to place the RIS module in an area which is typically in the near-field region of the at least one RF antenna, thereby further reducing the spatial requirements of the OTA measurement system according to the present disclosure.

[0051] In other words, the OTA measurement system can be configured as a Compact Antenna Test Range (CATR).

[0052] The at least one reflector can be stationary, i.e. the at least one reflector cannot be turned or rotated.

[0053] Optionally, the OTA measurement system can comprise an absorber element arranged between the at least one RF antenna and the RIS module, wherein the absorber element blocks a direct transmission path between the at least one antenna and the RIS module.

[0054] According to another aspect of the present invention, the OTA measurement system further comprises at least one Fresnel lens, wherein the at least one RF antenna, the at least one Fresnel lens and the adjustable position are arranged such that far-field conditions are provided at the RIS module and at the at least one RF antenna. Thus, far-field conditions at the RIS module and at the at least one antenna can be provided by the at least one Fresnel lens, which appropriately refracts the at least one RF signal and the at least one reflected RF signal. This allows to place the RIS module in an area which is typically in the near-field region of the at least one RF antenna, thereby further reducing the spatial requirements of the OTA measurement system according to the present disclosure.

[0055] In the above variants, the OTA measurement system can be established as an indirect far-field system.

[0056] In one embodiment of the present invention, the adjustable position is spaced apart from the at least one RF antenna such that the adjustable position is located in the far-field region of the at least one RF antenna. Thus, by the sufficient distance between the at least one RF antenna and the RIS module, far-field conditions at the at least one RF antenna and at the RIS module can be obtained. In other words, the OTA measurement system can be established as a direct far-field system.

[0057] The OTA measurement system can further comprise an anechoic chamber, wherein the at least one RF antenna and the RIS module are arranged within the anechoic chamber. Generally, the anechoic chamber reduces unwanted reflections within the OTA measurement system and also shields the OTA measurement system from external electromagnetic waves, thereby improving the accuracy of the measurement results, in particular the accuracy of the determined at least one reflection parameter, the determined one or more OTA reflection parameters, the determined monostatic OTA reflection pattern and / or the determined bistatic OTA reflection pattern.

[0058] According to the present application, the problem is also solved by an over-the-air (OTA) measurement method, which performs an OTA measurement by means of an OTA measurement system, in particular an OTA measurement system according to any of the above variants. The method comprises the following steps:

[0059] Setting a relative position of the RIS module by means of the positioner unit, wherein the relative position is a position of the RIS module relative to the at least one RF antenna;

[0060] - generating at least one RF signal by means of the signal generator module;

[0061] - transmitting the at least one RF signal by means of the at least one RF antenna towards the RIS module;

[0062] - receiving at least one reflected RF signal from the RIS module by means of the at least one RF antenna; and

[0063] - determining at least one reflection parameter based on the at least one RF signal and based on the at least one reflected RF signal by means of the signal processing module.

[0064] The OTA measurement system is configured such that a far-field condition of the at least one transmitted RF signal is provided at the RIS module and a far-field condition of the at least one reflected RF signal is provided at the at least one RF antenna. The at least one RF antenna comprises only one RF antenna or only one RF antenna array which is used as transmitter and receiver for the at least one RF signal at the same time.

[0065] In particular, the OTA measurement system according to any of the above variants is configured to perform the OTA measurement method.

[0066] With regard to further advantages and properties of the OTA measurement method, please refer to the above explanations with regard to the OTA measurement system, which are also applicable to the OTA measurement method and vice versa. BRIEF DESCRIPTION OF DRAWINGS

[0067] The above aspects and many attendant advantages of the claimed subject matter will become more readily apparent upon reference to the following detailed description when taken in conjunction with the drawings wherein:

[0068] - Figure 1 a first variant of an OTA measurement system according to the present application is schematically illustrated;

[0069] - Figure 2 a second variant of an OTA measurement system according to the present application is schematically illustrated;

[0070] - Figure 3 a third variant of an OTA measurement system according to the present application is schematically illustrated;

[0071] - Figure 4 a fourth variant of an OTA measurement system according to the present application is schematically illustrated;

[0072] - Figure 5 a flowchart of an OTA measurement method performed by the OTA measurement system of any one of Figures 1 to 4

[0073] - Figures 6 to 8 different figures illustrating the various steps of the OTA measurement method of Figure 5 DETAILED DESCRIPTION

[0074] The detailed description set forth below is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments in which the disclosed subject matter can be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the disclosed subject matter, and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not meant to be exhaustive or to limit the claimed subject matter to the precise forms disclosed.

[0075] For the purposes of this disclosure, the phrase "at least one of A, B, and C," for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C), including all further possible combinations when more than two elements are listed. In other words, the term "at least one of A and B" typically refers to "A and / or B," that is, either "A" alone, "B" alone, or "A" and "B" together.

[0076] Figure 1 An OTA measurement system 10 comprising a measurement instrument 12 and an anechoic chamber 14 is schematically illustrated.

[0077] Generally, the OTA measurement system 10 is configured to perform OTA measurements on a device under test, and more specifically, on a RIS module 16.

[0078] For example, the measurement instrument 12 can be a network analyzer, a vector network analyzer, or a spectrum analyzer. ​​

[0079] However, it should be appreciated that any other suitable type of measuring instrument, in particular any other suitable amplitude measuring instrument, can be used.

[0080] The measuring instrument 12 comprises a signal generator module 18 configured to generate an RF signal.

[0081] For example, the RF signal generated by the signal generator module 18 can be a continuous wave signal having a frequency corresponding to the operating frequency of the RIS module 16.

[0082] As another example, the RF signal generated by the signal generator module 18 can be a modulated signal having a carrier frequency corresponding to the operating frequency of the RIS module 16.

[0083] The measuring instrument 12 further comprises a coupling and / or switching module 20 connected to the signal generator module 18 so as to receive the RF signal generated by the signal generator module 18.

[0084] The measuring instrument 12 further comprises a receiver module 22 connected to the coupling and / or switching module 20.

[0085] Furthermore, the measuring instrument 12 comprises a signal processing module 24 connected to both the signal generator module 18 and the receiver module 22.

[0086] In general, the anechoic chamber 14 provides an undistorted or at least distortion-reduced environment for testing the RIS module 16.

[0087] Indeed, the anechoic chamber 14 can comprise a casing configured to shield the interior of the anechoic chamber 14 from external electromagnetic waves.

[0088] Furthermore, absorber elements can be provided inside the anechoic chamber 14 to reduce unwanted reflections within the anechoic chamber 14.

[0089] For testing, the RIS module 16 is placed in a positioner unit 26 located inside the anechoic chamber 14.

[0090] In general, the positioner unit 26 is configured to hold the RIS module 16 in an adjustable position suitable for testing the RIS module 16.

[0091] Indeed, the positioner unit 26 is configured to modify the adjustable position.

[0092] In Figure 1 In the exemplary embodiment shown, the positioner unit 26 is configured to modify the azimuth, the elevation and the height of the RIS module 16.

[0093] It is to be understood, however, that any other degree of freedom of the adjustable position of the RIS module 16 can be additionally or alternatively modified by the positioner unit 26.

[0094] The OTA measurement system 10 further comprises at least one RF antenna 28 arranged in the anechoic chamber 14.

[0095] In Figure 1 In the exemplary embodiment shown, the at least one RS antenna 28 is a single RF antenna.

[0096] Generally, the RF antenna 28 is configured to transmit the RF signal generated by the signal generator module 18 to the RIS module 16 and to receive the corresponding reflected RF signal from the RIS module 16.

[0097] The RF antenna 28 is coupled to the signal generator module 18 via the coupling and / or switching module 20, which forwards the RF signal generated by the signal generator module 18 to the RF antenna 28.

[0098] Further, the RF antenna 28 is connected to the receiver module 22 via the coupling and / or switching module 20, which forwards the reflected RF signal received by the RF antenna 28 to the receiver module 22.

[0099] As described above, the positioner unit 26 is configured to hold the RIS module 16 in an adjustable position.

[0100] The adjustable position is selected such that far-field conditions for the transmitted RF signal are obtained at the RIS module 16 and such that far-field conditions for the reflected RF signal are obtained at the RF antenna 28.

[0101] In Figure 1 In the exemplary embodiment shown, the OTA measurement system 10 is established as a direct far-field system, i.e. the far-field conditions are obtained by a sufficient distance between the RF antenna 28 and the RIS module 16.

[0102] In the following, a plurality of exemplary embodiments of the OTA measurement system 10 are described, which are established as indirect far-field systems.

[0103] Figure 2 Another exemplary embodiment of the OTA measurement system 10 is shown, wherein only the differences compared to the first variant described above with reference to Fig. 1 are explained in the following. Figure 1

[0104] In this exemplary embodiment, a Fresnel lens 30 is arranged between the RF antenna 28 and the RIS module 16.

[0105] ​The RF antenna 28, the Fresnel lens 30 and the RIS module 16 are arranged such that far field conditions are provided at the RIS module 16 as well as at the RF antenna 28.

[0106] In this embodiment, the RIS module 16 can be placed in an area which is typically a near field area of the RF antenna 28.

[0107] However, the transmitted RF signals as well as the reflected RF signals are refracted by the Fresnel lens 30 such that far field conditions are obtained at the RIS module 16 as well as at the RF antenna 28.

[0108] Figure 3 Another exemplary embodiment of the OTA measurement system 10 is shown, wherein only the differences compared to the above variants will be explained in the following.

[0109] In this exemplary embodiment, a single RF antenna array 32 is provided instead of the RF antenna 28.

[0110] The RF antenna array 32 is configured as a plane wave converter and the RIS module 16 is arranged in a quiet zone of the RF antenna array 32.

[0111] Far field conditions of the RF signals transmitted by the RF antenna array 32 at the RIS module 16 as well as far field conditions of the RF signals reflected at the RF antenna array 32 are synthesized by the RF antenna array 32 which is configured as a plane wave converter.

[0112] Thus, the RIS module 16 can be placed in an area which is typically a near field area of the RF antenna 28.

[0113] Figure 4 Another exemplary embodiment of the OTA measurement system 10 is shown, wherein only the differences compared to the above variants will be explained in the following.

[0114] In this exemplary embodiment, the OTA measurement system 10 is established as a compact antenna test range (CATR) with a reflector 34 arranged in the anechoic chamber 14.

[0115] The reflector 34 is arranged and configured such that the RF signals transmitted by the RF antenna 28 are forwarded to the RIS module 16 and such that the reflected RF signals are forwarded to the RF antenna 28.

[0116] The RF antenna 28, the reflector 34 and the RIS module 16 are arranged such that far field conditions are provided at the RIS module 16 as well as at the RF antenna 28.

[0117] The reflector 34 can be static, i.e. the at least one reflector is not rotatable or swivelable.

[0118] However, it is also conceivable that the reflector 34 is rotatable.

[0119] Optionally, the OTA measurement system 10 can comprise an absorber element 36 arranged between the RF antenna 28 and the RIS module 16, wherein the absorber element 36 blocks a direct transmission path between the RF antenna 28 and the RIS module 16.

[0120] The OTA measurement system 10 according to any of the above variants is configured to perform the below described OTA measurement method. Figure 5

[0121] In the following, the term “relative position” refers to the position of the RIS module 16 relative to the RF antenna 28 or relative to the RF antenna array 32.

[0122] The relative position of the RIS module 16 is set by the positioner unit 26, and the RF signal is generated by the signal generator module 18 (step S1).

[0123] The generated RF signal is forwarded to the RF antenna 28 or to the RF antenna array 32 via the coupling and / or switching module 20.

[0124] Further, the generated RF signal is forwarded to the signal processing module 24 as a reference signal.

[0125] The RF signal is transmitted by the RF antenna 28 or by the RF antenna array 32 to the RIS module 16, and the corresponding reflected RF signal is received by the RF antenna 28 or by the RF antenna array 32 (step S2).

[0126] The reflected RF signal is forwarded to the receiver module 22 via the coupling and / or switching module 20.

[0127] The receiver module 22 suitably processes the reflected RF signal and forwards the reflected RF signal to the signal processing module 24.

[0128] The signal processing module 24 determines at least one reflection parameter based on the RF signal and based on the reflected RF signal (step S3).

[0129] In particular, the determined at least one reflection parameter can be or comprise at least one S-parameter or any other suitable type of reflection parameter.

[0130] For example, the determined at least one reflection parameter can comprise a parameter of the amplitude S11 (in particular measured with a vertical polarization of the RF signal) and a parameter of the amplitude S22 (in particular measured with a horizontal polarization of the RF signal).

[0131] Without limiting generality, exemplary cases are described in the following where the at least one reflection parameter is an S-parameter.​

[0132] The OTA reflection parameter of the RIS module 16 is determined by the signal processing module 24 based on the determined at least one reflection parameter (step S4).

[0133] As Figure 6 illustrated, this diagram shows a plot of the reflection S parameter plotted against time, the at least one reflection parameter including not only the contribution from the desired reflection of the RF signal at the RIS module 16 back to the RF antenna 28 or RF antenna array 32, which is marked in Figure 6 by the time window 38.

[0134] Instead, the at least one reflection parameter includes other contributions 40, e.g. due to reflections of the RF signal from other surfaces or due to multiple reflections within the OTA measurement system 10.

[0135] The signal processing module 24 can be configured to extract the desired contribution to the at least one reflection parameter by applying a suitable time gating algorithm to determine the OTA reflection parameter, in particular wherein the signal processing module is configured to apply a time gating algorithm to the reflected RF signal in order to determine the OTA reflection parameter.

[0136] For example, a window function such as a Hann window can be applied to the reflected RF signal in order to isolate the desired reflection.

[0137] By applying such a time gating algorithm, the absorber element 36 described above with respect to Figure 4 is optional, as the direct reflection can be discarded due to the different travel times of the RF signal via the reflector 34 compared to the direct path between the RF antenna 28 and the RIS module 16.

[0138] Alternatively, the at least one background reflection parameter can be determined without the RIS module 16 being placed in the localizer unit 26, and the at least one background reflection parameter can be subtracted from the at least one reflection parameter determined with the RIS module 16 being placed in the localizer unit 26, thereby obtaining the OTA reflection parameter.

[0139] The above steps S1 to S4 are repeated for a plurality of different relative positions of the RIS module 16, thereby obtaining a monostatic OTA reflection pattern of the RIS module 16 (step S5).

[0140] In other words, the localizer unit 26 successively modifies the adjustable position to a set of different positions, and determines the OTA reflection parameter at the different positions, respectively.

[0141] For example, the azimuth and / or the elevation of the RIS module 16 can be adjusted between the different positions.

[0142] The final angular distribution 42 of the OTA reflection parameters (e.g. Figure 7 ) is the monostatic OTA reflection mode of the RIS module 16.

[0143] Figure 7 The exemplary results shown were obtained with a horizontal polarization of the RF signal at a frequency of 28 GHz.

[0144] However, it should be understood that, as already described above, the operating frequency of the RIS module 16 and therefore the frequency of the RF signal may have any other arbitrary value.

[0145] Figure 7 Also illustrated are raw measurement data 44 of at least one reflection parameter, wherein no time gating algorithms or other corrections are applied to the reflection parameters determined at different locations.

[0146] The bistatic OTA reflection pattern of the RIS module 16 is determined by the signal processing module 24 based on the determined monostatic OTA reflection pattern (step S6).

[0147] More specifically, the signal processing module 24 may be configured to apply Falconer's monostatic to bistatic equivalence theorem to the determined monostatic OTA reflection pattern in order to determine the bistatic OTA reflection pattern for the RIS module 16 .

[0148] Falconer's monobasic to bibasic equivalence theorem converts the bibasic cross section σ b With the single base cross section σ m Connected, according to:

[0149]

[0150] Among them, such as Figure 8 As shown, θ is the equivalent single-base elevation angle (i.e. Figure 8 The angle relative to the z-axis, θ r is the bistatic receiver elevation angle, θ t is the bistatic transmitter elevation angle, and f is the transmitter frequency.

[0151] Falconer's monostatic to bistatic equivalence theorem describes the conversion from a monostatic cross section to a bistatic cross section for one dimension (ie, elevation angle).

[0152] In a generalized approach, the bistatic OTA reflection pattern of the RIS module 16 may be determined using the generalized monostatic to bistatic equivalence theorem, which describes the conversion from a monostatic cross section to a bistatic cross section for two dimensions (ie, azimuth and elevation).

[0153] The generalized monobasic to bibasic equivalence theorem converts the bibasic cross section σb With the single base cross section σ m Connected, according to:

[0154]

[0155] Among them, θ m is the equivalent monostatic elevation angle (i.e., Figure 8 The angle relative to the z-axis, θ r is the bistatic receiver elevation angle, θ t is the bistatic transmitter elevation angle, φ m is the equivalent single-base azimuth (i.e., Figure 8 The angle in the xy plane relative to the x-axis), φ r is the bistatic receiver azimuth, and φ t is the bistatic transmitter azimuth.

[0156] Therefore, the generalized monostatic to bistatic equivalence theorem allows for arbitrary transmitter and receiver azimuths.

[0157] Certain embodiments disclosed herein, particularly corresponding one or more modules and / or one or more units, utilize circuitry (e.g., one or more circuits) to implement the standards, protocols, methods, or techniques disclosed herein, operatively couple two or more components, generate information, process information, analyze information, generate signals, encode / decode signals, convert signals, transmit and / or receive signals, control other devices, etc. Any type of circuitry may be used.

[0158] In one embodiment, the circuit includes, among other things, one or more computing devices such as a processor (e.g., a microprocessor), a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a system on a chip (SoC), etc., or any combination thereof, and may include discrete digital or analog circuit elements or electronic devices, or a combination thereof. In one embodiment, the circuit includes a hardware circuit implementation (e.g., an analog circuit implementation, a digital circuit implementation, etc., and a combination thereof).

[0159] In one embodiment, the circuitry comprises a combination of circuitry and a computer program product having software or firmware instructions stored on one or more computer-readable memories that work together to cause a device to perform one or more protocols, methods, or techniques described herein. In one embodiment, the circuitry comprises circuitry that requires software, firmware, etc. to operate, such as, for example, a microprocessor or portion of a microprocessor. In one embodiment, the circuitry comprises one or more processors or portions thereof and associated software, firmware, hardware, etc.

[0160] This application can refer to quantities and numbers. Unless specifically stated, these quantities and numbers should not be considered limiting but rather as examples of possible quantities or numbers associated with this application. Also in this regard, this application can use the term "a plurality" to refer to quantities or numbers. In this regard, the term "a plurality" means any number more than one, such as two, three, four, five, etc. The terms "about," "approximately," "near," and the like mean plus or minus 5% of the stated value.

Claims

1. An over-the-air, OTA, measurement system for testing a reconfigurable intelligent surface, RIS, wherein the OTA measurement system (10) comprising at least one signal generator module (18), wherein the at least one signal generator module (18) is configured to generate at least one radio frequency, RF, signal, wherein the OTA measurement system (10) further comprises at least one RF antenna (28), wherein the at least one RF antenna (28) is connected to the at least one signal generator module (18) in order to receive at least one RF signal, wherein the at least one RF antenna (28) is configured to emit the at least one RF signal, wherein the OTA measurement system (10) further comprises a positioner unit (26) configured to hold a RIS module (16) in an adjustable position, wherein the positioner unit (26) is configured to modify the adjustable position, wherein the at least one RF antenna (28) is further configured to receive at least one reflected RF signal, wherein the at least one reflected RF signal corresponds to the at least one RF signal reflected by the RIS module (16), wherein the at least one RF antenna (28) comprises only one RF antenna (28) or only one RF antenna array (32) that functions as an emitter and receiver for the at least one RF signal, wherein the OTA measurement system (10) is configured such that far-field conditions of at least one emitted RF signal are provided at the RIS module (16) and such that far-field conditions of the at least one reflected RF signal are provided at the at least one RF antenna (28), wherein the OTA measurement system (10) further comprises at least one receiver module (22) connected to the at least one RF antenna (28) in order to receive the at least one reflected RF signal from the at least one RF antenna (28), and wherein the OTA measurement system (10) further comprises a signal processing module (24), wherein the signal processing module (24) is configured to determine at least one reflection parameter based on the at least one RF signal and based on the at least one reflected RF signal.

2. The OTA measurement system of claim 1, wherein, The positioner unit (26) is configured to adjust an azimuth angle, an elevation angle and / or a height of the RIS module (16).

3. The OTA measurement system of any of the preceding claims, wherein, The signal processing module (24) is configured to determine an OTA reflection parameter of the RIS module (16) based on the at least one reflection parameter.

4. The OTA measurement system of claim 3, wherein, The signal processing module (24) is configured to apply a time-gating algorithm in order to determine the OTA reflection parameter, in particular wherein the signal processing module is configured to apply the time-gating algorithm to the reflected RF signal in order to determine the OTA reflection parameter.

5. The OTA measurement system of claim 3 or 4, wherein, The positioner unit (26) is configured to modify the adjustable position continuously to a set of different positions, and wherein the signal processing module (24) is configured to determine the OTA reflection parameter at the different positions, in particular at each of the different positions, respectively.

6. The OTA measurement system of claim 5, wherein, The signal processing module (24) is configured to determine a monostatic OTA reflection pattern of the RIS module (16) based on the determined OTA reflection parameters at the different positions.

7. The OTA measurement system of claim 6, wherein, The signal processing module (24) is configured to determine a bistatic OTA reflection pattern of the RIS module (16) based on the determined monostatic OTA reflection pattern, in particular by applying Falconer’s monostatic-to-bistatic equivalence theorem or a generalized monostatic-to-bistatic equivalence theorem to the determined monostatic OTA reflection pattern.

8. The OTA measurement system according to any of the preceding claims, further comprising a measuring instrument (12), wherein, The measuring instrument (12) comprises the at least one signal generator module (18), the at least one receiver module (22) and / or the signal processing module (24), in particular wherein the measuring instrument (12) is a network analyzer, a vector network analyzer or a spectrum analyzer.

9. The OTA measurement system of any of the preceding claims, wherein, The at least one RF signal generated by the at least one signal generator module (18) is a continuous wave, CW, signal or a modulated signal.

10. The OTA measurement system of any of the preceding claims, wherein, The at least one RF antenna (28) comprises only one RF antenna array (32), wherein the RF antenna array (32) is configured as a plane wave converter, and wherein the adjustable position is located in a quiet zone of the RF antenna array (32).

11. The OTA measurement system according to any of the preceding claims, further comprising at least one reflector (34), wherein, The at least one reflector (34) is arranged and configured such that the at least one RF signal emitted by the at least one RF antenna (28) is forwarded to the RIS module (16), wherein the at least one reflector (34) is arranged and configured such that the at least one reflected RF signal is forwarded to the at least one RF antenna (28), and wherein the at least one RF antenna (28), the at least one reflector (34) and the adjustable position are arranged such that far-field conditions at the RIS module (16) and at the at least one RF antenna (28) are provided.

12. The OTA measurement system according to any of the preceding claims, further comprising at least one Fresnel lens (30), wherein, The at least one RF antenna (28), the at least one Fresnel lens (30) and the adjustable position are arranged such that far-field conditions at the RIS module (16) and at the at least one RF antenna (28) are provided.

13. The OTA measurement system of any one of claims 1 to 9, wherein, The adjustable position is spaced apart from the at least one RF antenna (28) such that the adjustable position is located in a far-field region of the at least one RF antenna (28).

14. An over-the-air (OTA) measurement method, the method comprising the following steps: - setting a relative position of a RIS module (16) by a positioner unit (26), wherein the relative position is a position of the RIS module (16) relative to at least one RF antenna (28); - generating at least one RF signal by a signal generator module (18); - emitting the at least one RF signal by the at least one RF antenna (28) towards the RIS module (16); - determining an OTA reflection parameter at the RIS module (16) by a receiver module (22) of the OTA measurement system (10); and - determining a bistatic OTA reflection pattern of the RIS module (16) based on the determined monostatic OTA reflection pattern, in particular by applying Falconer’s monostatic-to-bistatic equivalence theorem or a generalized monostatic-to-bistatic equivalence theorem to the determined monostatic OTA reflection pattern. - receiving, by the at least one RF antenna (28), at least one reflected RF signal from the RIS module (16); and - determining, by the signal processing module (24), at least one reflection parameter based on the at least one RF signal and based on the at least one reflected RF signal, wherein the OTA measurement system (10) is configured such that far-field conditions of the at least one transmitted RF signal are provided at the RIS module (16) and far-field conditions of the at least one reflected RF signal are provided at the at least one RF antenna (28), and wherein the at least one RF antenna (28) comprises only one RF antenna (28) or only one RF antenna array (32) that functions as both a transmitter and a receiver for the at least one RF signal.

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