Arrangement for measuring the transfer function over a path from a feed antenna via a reflector to a radar sensor test zone

Abstract

The invention relates to an arrangement for measuring the transmission function on a path from a feed antenna (1) via a reflector (2) to a radar sensor test zone (3), said arrangement being provided with an absorber chamber (4), wherein the feed antenna (1) is designed to emit and receive a radar signal and is arranged together with the reflector (2) inside the absorber chamber (4), and the radar sensor test zone (3) is a predefined region inside the absorber chamber (4) in which a radar sensor (5) to be tested is intended to be tested by means of a radar signal emitted by the feed antenna (1) with the aid of a radar target simulator (6), characterised in that a retroreflector (7) is arranged in the radar sensor test zone (3) in order to reflect, in the radar frequency range, at least one part of a measurement signal, that is received from the feed antenna (1) via the reflector (2), back to the feed antenna (1) via the reflector (2). This allows for a high-precision measurement of the transmission function on the path from the feed antenna (1) via the reflector (2) to the radar sensor test zone (3) in the absorber chamber (4).

Description

[0001] Arrangement for measuring the transfer function on a path from a feed antenna via a reflector to a radar sensor test zone

[0002] The invention relates to an arrangement for measuring the transfer function on a path from a feed antenna via a reflector to a radar sensor test zone, comprising an absorber chamber, wherein the feed antenna is designed to transmit and receive a radar signal and is arranged together with the reflector within the absorber chamber, and the radar sensor test zone is a predetermined area within the absorber chamber in which a radar sensor to be tested is to be tested by means of a radar signal transmitted by the feed antenna with the aid of a radar target simulator.

[0003] The simulation of radar targets and radar echoes for automotive radar sensors at the physical level using radar target simulators based on the over-the-air principle is well known from the state of the art. Radar sensors play an important role in the integration of solutions for assisted and autonomous driving in motor vehicles. Corresponding radar target simulators are used to ensure the correct function of sensors and developed application software during various phases of the development, production, and release process for sensors and vehicles, as well as for use in the aftermarket. Such radar target simulators enable radar sensors to be tested in the laboratory in clearly defined, reproducible scenarios. Object reflections, so-called radar targets, which occur in road traffic at different distances, speeds, and sizes, are simulated in real time.Such tests play a crucial role in the validation of radar-based driver assistance systems and autonomous vehicles. The associated radar target simulators are available for development and testing in the laboratory, for end-of-line testing in production, for vehicle homologation, and for the spare parts business.

[0004] The radar target simulators in question operate according to the over-the-air principle mentioned above: A real radar sensor is excited in real time during operation. The radar target simulator receives the signal from the radar sensor, generates an internal echo, and sends it back to the radar sensor. This allows the radar sensor to be operated and tested just as it would in a real environment. To test the sensor in a defined manner, extensive manipulation of the echoes is possible: By delaying the echo, the distance of an object or target is simulated, by changing the frequency, its speed is simulated, and by attenuating the reflected energy, the object size is simulated. To determine the azimuth angle, the receiver and transmitter modules can be positioned and moved differently. Alternatively, a system with multiple receiver and transmitter modules can be set up.With a mechatronic extension solution, continuous angle simulation is also possible.

[0005] With such radar target simulators, developers of ADAS / AD (Advanced Driver Assistance Systems / Autonomous Driving) applications can perform required tests quickly, efficiently, and thoroughly. This is made possible by highly precise, reliable echo generation combined with flexible options for supporting relevant use cases. Object detection scenarios such as Adaptive Cruise Control (ACC), Autonomous Emergency Braking (AEB), pedestrian detection, and cut-in / cut-out maneuvers can be realistically simulated with these radar target simulators.

[0006] An end-of-line (EOL) test bench for mass-produced automotive radar sensors is typically used to test the functionality of fully assembled assemblies and to calibrate them automatically within a compact, low-reflection anechoic chamber using radar target simulation. The measurement of the operating parameters of the radar sensors under test (RUT) and their calibration are performed in a defined test sequence in which the radar sensor is rotated horizontally and vertically around its radiation center using high-precision drives.

[0007] In a Compact Antenna Test Range (CATR) of an EOL test bench for testing radar control units, a feed antenna and a reflector must be precisely aligned to each other. The goal is to generate the most flat electromagnetic field possible in the area where the RUT is placed. This area is called the quiet zone and will also be referred to below as the radar sensor test zone. Since the mechanical pre-alignment of the components is only possible with a finite degree of accuracy, the result must be determined by measuring the transfer function from the feed antenna to the quiet zone using a network analyzer. The transfer function is complex-valued. Using the amplitude and phase of the transfer function over various locations in the quiet zone, the alignment of the components can be evaluated and any necessary correction determined.

[0008] Corrections can be made, for example, by mechanically aligning the feed antenna and CATR reflector. The goal here is to position the feed antenna exactly at the focal point of the reflector. A second possible correction is to change the position of the RUT. If the number of degrees the phase front is tilted is known, the RUT can be tilted by this angle so that it is exposed to a plane wave. Furthermore, corrections can also be made during the evaluation of the data obtained with the RUT. The RUT usually has several transmit and receive antennas. By appropriately controlling the antennas, the line of sight of the RUT can be determined. A known misalignment can then be calculated when evaluating the data recorded by the RUT, for example by applying different time delays to the data from the different receive antennas.

[0009] This gives rise to the following technical problems: To measure directly in the quiet zone, a receiving unit is currently placed there. This unit must be connected to a measuring device outside the anechoic chamber by cables. This means that long cables must be run into the closed anechoic chamber. This requires a certain amount of conversion work. Furthermore, the presence of cables in the anechoic chamber can influence the measurements. Furthermore, since the receiving unit is moved to different positions in the quiet zone for measurement, the cables are also moved. This movement influences the phase of the measured signal. It is no longer possible to subsequently separate these phase changes from the phase of the transfer function being measured.

[0010] In practice, the measuring cables are currently routed through an additional opening into the anechoic chamber. To minimize the influence on the measurement, the cables are often connected to the receiving unit in a loop on the side facing away from the reflector. The influence of the cable movement on the phase is accepted.

[0011] DE 10 2022 115 284 A1 describes that a test signal is generated in test mode using a test signal unit, and the test signal or a test signal derived from the test signal is emitted as an output signal via the emitting element, wherein an evaluation unit evaluates the received signal or the derived received signal with regard to its phase position and / or amplitude synchronously with the emission of the test signal or the derived test signal as an output signal and stores the determined value for the phase position and / or amplitude. By providing the test signal unit, it is possible to generate a test signal if necessary and to emit it into the exterior via the emitting element. This was not previously possible with other test devices, as they merely re-emit previously received signals with a corresponding time delay.

[0012] The measures outlined in DE 10 2022 115 284 A1 make it possible to leave the test fixture for testing a distance sensor test bench in its installed position; the test fixture therefore no longer needs to be replaced by a special transmitter. The principle is that the transmitted test signal or the test signal derived from the test signal is reflected in the arrangement of the distance sensor test bench and received again by the test fixture. The received signal then received by the test fixture corresponds to the transmitted and reflected test signal during test operation. This received signal or the received signal derived from it can then be evaluated by the evaluation unit with regard to its phase position and / or amplitude. The evaluation is usually carried out with reference to a reference signal. This can be, for example, the transmitted test signal.

[0013] The object of the invention is to provide a highly precise measurement of the transfer function along a path from a feed antenna via a reflector to a radar sensor test zone in an anechoic chamber. This object is achieved by the subject matter of the independent patent claims. Preferred developments can be found in the subclaims.

[0014] According to the invention, an arrangement for measuring the transfer function on a path from a feed antenna via a reflector to a radar sensor test zone, comprising an absorber chamber, is proposed, wherein the feed antenna is designed to transmit and receive a radar signal and is arranged together with the reflector within the absorber chamber, and the radar sensor test zone is a predetermined area within the absorber chamber in which a radar sensor to be tested is to be tested by means of a radar signal transmitted by the feed antenna with the aid of a radar target simulator, wherein a retroreflector is arranged in the radar sensor test zone in order to reflect at least part of a measurement signal in the radar frequency range received by the feed antenna via the reflector back to the feed antenna via the reflector.

[0015] An anechoic chamber is a defined environment with absorbers for electromagnetic waves mounted on its metallic, electrically conductive walls. The anechoic chamber differs from the anechoic chambers commonly used in acoustics in that the absorbers on its walls are capable of absorbing electromagnetic waves, not sound waves.

[0016] A retroreflector is a device that largely reflects incident electromagnetic radiation in the direction from which it came, regardless of its direction of incidence relative to the device's orientation. For example, a retroreflector is a corner cube.

[0017] The measurement signal is a signal whose frequency lies in the radar frequency range. However, it does not have to be a usable radar signal itself, such as a chirp signal. The portion of the measurement signal received by the feed antenna due to backreflection is also referred to below as the measurement signal received by the feed antenna. A key aspect of the invention is that a retroreflector is placed in the quiet zone instead of the receiving unit. This eliminates the need to route measurement cables into the interior of the anechoic chamber. The incident electromagnetic wave is reflected at the retroreflector in the direction from which it came. The reflected wave travels via the reflector back to the feed antenna, where it can be measured. This method measures the transfer function of the double path. To obtain the transfer function of the single path, the measured values ​​are subsequently converted:

[0018] Since the phase of a propagating electromagnetic wave is linearly related to the distance traveled, traveling twice the distance results in twice the phase compared to traveling once. Therefore, to obtain the phase of the single-path transfer function, the measured phase value must be divided by a factor of 2. The amplitude is inversely proportional to the squared distance traveled. The single-path transfer function corresponds to Harald Friis's transfer formula. The transfer function measured using the described approach corresponds to the radar equation. The conversion is performed using a factor that can be calculated from the radar cross-section of the retroreflector used and the air distance.

[0019] Among other advantages, the invention eliminates the need to install additional measuring cables in the anechoic chamber, which could influence the measurement results through their presence or movement. This improves the signal quality of the measurement results. Furthermore, the acquisition costs for the measuring cables are eliminated. Furthermore, no modification of the anechoic chamber is necessary to provide a cable entry for the measuring cables.

[0020] A particularly preferred embodiment of the arrangement according to the invention is that it comprises a network analyzer connected to the feed antenna, which is configured, on the one hand, to apply the measurement signal to the feed antenna so that it is emitted by the feed antenna, and, on the other hand, to receive a portion of the measurement signal reflected back by the feed antenna so that this or a measurement signal derived therefrom can be evaluated. The measurement signal does not have to be a radar signal with which the radar sensor to be tested subsequently typically operates. Rather, the measurement signal can also be a simple, monofrequency signal in the form of a sine wave.The network analyzer preferably transmits such a sinusoidal signal of a specific frequency step by step, and after evaluating the measurement at this frequency, a next frequency is set and transmitted so that a total frequency range can be covered that is of interest for the respective testing of a radar sensor.

[0021] Furthermore, a preferred embodiment of the invention provides that the arrangement itself already has an evaluation device configured to determine the transfer function from the feed antenna to the retroreflector. This evaluation device can be part of the network analyzer or provided separately.

[0022] According to a preferred development of the invention, the arrangement further comprises a time-gating device configured to differentiate between signals received by the network analyzer with regard to their propagation times. The background to this preferred embodiment of the invention is that it cannot be ruled out that a reflection may occur when the signal is coupled into the feed antenna. This would overlap with the measured signal. The reflected signal and the measurement signal would then also lie in the same frequency range and therefore could not be separated by a filter. In this respect, the possibility of separating the signals by windowing in the time domain (time gating) is proposed. In this way, the signals can be differentiated from one another by their different propagation times.Preferably, the measured frequency-domain data is transformed into the time domain using inverse Fourier transformation. A specific time range is then selected using a window function. The windowed signal is then transformed back into the frequency domain. The processed signal then contains the information about the desired transfer function.

[0023] In principle, the arrangement according to the invention can be operated without an amplifier. However, according to a preferred embodiment of the invention, the network analyzer is provided with an input for receiving the reflected measurement signal from the feed antenna, which is preceded by an amplifier. This makes it possible to detect even small signals.

[0024] Furthermore, a preferred development of the invention provides that the arrangement comprises a transmit frequency converter for applying the measurement signal to be transmitted to the feed antenna and a receive frequency converter for receiving the reflected portion of the measurement signal. The frequency converters are preferably high-bandwidth converters. High-bandwidth converters are characterized by their compact design. For example, the high-bandwidth converters included in the DARTS 9040-G device from dSPACE can be used. Furthermore, it is preferred that the transmit frequency converter be configured to convert the measurement signal to a higher frequency, and the receive frequency converter be configured to convert the measurement signal to a lower frequency.In this context, it is particularly preferred that the higher frequency be greater than 6 GHz, preferably at least 24 GHz, and the lower frequency be less than 6 GHz. Radar signals in the automotive sector typically range between 24 GHz and 81 GHz.

[0025] The present invention is concerned with measuring the aforementioned transfer function in order to be able to know and take it into account in a subsequent test of a radar sensor using a radar target simulator. In this context, according to a preferred development of the invention, a transmit frequency converter and a receive frequency converter of the radar target simulator are used as the transmit frequency converter and the receive frequency converter, respectively, with which the radar sensor to be tested later or subsequently is to be tested. Thus, the already existing frequency converters of the radar target simulator are used. In this context, the frequency converters of the radar target simulator are preferably supplied with a DC voltage and a local oscillator signal for a respective frequency converter in the respective frequency converter.

[0026] To check the alignment of the system in question, there is no need to dismantle the radar target simulator's frequency converter in order to use it as a measuring receiver in the quiet zone, i.e., the radar sensor test zone. This reduces the conversion effort, as only the retroreflector needs to be installed. With a major conversion, there is always the risk of accidentally damaging or incorrectly connecting parts. A further advantage is that when using the radar target simulator's frequency converter in the measurement setup, the signal does not have to be measured in the frequency range up to 81 GHz, which would only be possible with very expensive measuring devices. With the method proposed here, a network analyzer for frequencies below 6 GHz can be used. This way, a mobile measuring device can be used instead of a large laboratory device.

[0027] According to a preferred development of the invention, a coupler is connected between the feed antenna, on the one hand, and the transmit frequency converter and the receive frequency converter, on the other hand, which coupler is configured to separate the received measurement signal from the transmitted measurement signal. Furthermore, it is preferred that a bandpass filter is connected between the transmit frequency converter and the coupler, which is configured such that only measurement signals within a predetermined frequency range can be transmitted with the feed antenna. This is advantageous in that it reduces or completely prevents the superposition of signals from outside the frequency band on the receive side with the useful signals during conversion.

[0028] In principle, it is possible to connect the transmit frequency converter and the bandpass filter directly to each other. However, according to a preferred embodiment of the invention, an isolator is connected between the transmit frequency converter and the bandpass filter to attenuate reflected signals coming from the direction of the bandpass filter and the coupler, preventing them from being redirected back to the transmit frequency converter. This reduces or prevents unwanted resonance phenomena caused by reflected signals, which could otherwise reduce the power of the transmitted measurement signal.

[0029] Finally, according to a preferred embodiment of the invention, the retroreflector is attached to a movable robot arm. This enables simple and precise repositioning of the retroreflector. Furthermore, the invention also relates to a method for measuring the transfer function along a path from a feed antenna via a reflector to a radar sensor test zone in an anechoic chamber, comprising the following steps:

[0030] Emitting a measurement signal in the radar frequency range from the feed antenna via the reflector into the radar sensor test zone,

[0031] Reflecting at least a portion of the measurement signal emitted into the radar sensor test zone back to the feed antenna via the reflector by means of a retroreflector arranged in the radar sensor test zone.

[0032] According to a preferred development of the method according to the invention, the portion of the measurement signal received due to back reflection from the feed antenna and a reflection signal generated when the measurement signal is coupled into the feed antenna are separated by windowing in the time domain. In this context, it is particularly preferred that the method comprises the following method steps:

[0033] Transforming the frequency domain data of the received part of the measurement signal and the frequency domain data of the reflection signal generated when the measurement signal is coupled into the feed antenna by means of inverse Fourier transformation from the frequency domain to the time domain in a time gating device,

[0034] Selecting a predetermined time range which, on the one hand, contains the time composed of the expected propagation time of the measurement signal on the route from the feed antenna via the reflector to the retroreflector and back as well as the propagation time of the measurement signal from the feed antenna to the time gating device, and which, on the other hand, does not contain the expected propagation time of the reflection signal from the feed antenna to the time gating device, so that a windowed time signal is obtained, and

[0035] Transforming the windowed time signal from the time domain back to the frequency domain.

[0036] As explained above, it cannot be ruled out that a reflection will occur when the signal is coupled into the feed antenna, which would then overlap with the measured signal. Both signals would then be in the same frequency range and thus could not be separated by a filter. Therefore, it is preferable to separate the signals by windowing in the time domain in a time-gating device in order to distinguish the signals by their different propagation times. The signal obtained by transforming the windowed time signal from the time domain back to the frequency domain then contains the information about the desired transfer function.

[0037] Further preferred embodiments of the method according to the invention result in analogy to the preferred developments of the arrangement according to the invention mentioned above.

[0038] The invention is explained in more detail below using a preferred embodiment with reference to the drawings.

[0039] The drawings show

[0040] Fig. 1 shows schematically an arrangement for testing a radar sensor using a radar target simulator,

[0041] Fig. 2 schematically shows an arrangement for measuring the transfer function on a path from a feed antenna via a reflector to a radar sensor test zone according to a preferred embodiment of the invention,

[0042] Fig. 3 schematically shows the arrangement from Fig. 2 with further details,

[0043] Fig. 4 schematically shows a network analyzer according to a preferred embodiment of the invention and

[0044] Fig. 5 is a flowchart of a method according to a preferred embodiment of the invention.

[0045] Fig. 1 schematically shows an arrangement for testing a radar sensor 5 in the radar sensor test zone 3 in an absorber chamber 4. The absorber chamber 4 has metallic, electrically conductive walls, to which electromagnetic wave absorbers (not shown here) are attached. The absorber chamber 3 is also provided with a door (also not shown here for the sake of clarity), through which the interior of the absorber chamber 4 is accessible and with which the absorber chamber 4 can be closed during actual testing.

[0046] During testing, a radar target simulator 6 simulates, in real time, object reflections, so-called radar targets, which occur in road traffic at different distances, speeds, and sizes, in response to radar signals received by the radar sensor under test. Such radar signals are received and transmitted via a feed antenna 1 arranged in the absorber chamber 4, with the path between the feed antenna 1 and the radar sensor 5 arranged in the radar sensor test zone 3 passing through a reflector 2.

[0047] Since the mechanical pre-alignment of the components feed antenna 1, reflector 2, and radar sensor 5 is only possible with finite accuracy, the complex-valued transfer function from feed antenna 1 via reflector 2 to radar sensor 5 in radar sensor test zone 3 must be determined. Using the amplitude and phase of the transfer function across different locations in radar sensor test zone 3, the alignment of the components can be evaluated and any necessary correction determined. As already explained at the beginning, the necessary corrections can be made, for example, by mechanically aligning feed antenna 1 and reflector 2. The goal here is to position feed antenna 1 precisely at the focal point of reflector 2. Another possible correction is to change the positioning of radar sensor 5 under test, e.g., by tilting it so that it is exposed to a plane wave.Finally, a correction can also be made during the evaluation of the data obtained with the radar sensor 5 under test. Typically, the radar sensor 5 has multiple transmitting and receiving antennas that can be controlled differently, allowing the viewing direction of the radar sensor 5 to be determined. A known misalignment of the radar sensor 5 can then be computationally accounted for during the evaluation of the data recorded by the radar sensor 5, for example, by applying different time delays to the data from the different receiving antennas. In order to provide a highly precise measurement of the transfer function on the path from the feed antenna 1 via the reflector 2 to the radar sensor test zone 3 in the absorber chamber 4, an arrangement is used as schematically shown in Fig. 2.The feed antenna 1, which is designed to transmit and receive a radar signal, is arranged together with the reflector 2 within the absorber chamber. Instead of a sensor, a retroreflector 7 is arranged in the radar sensor test zone 3 to reflect at least part of a measurement signal in the radar frequency range received by the feed antenna 1 via the reflector 2 back to the feed antenna 1 via the reflector 2. The retroreflector 7 is attached to a robot arm 17, which is movable by means of a positioning system 18. The other components 19 of this arrangement can be seen, among other things, in Fig. 3.

[0048] As schematically shown in Fig. 3, the arrangement comprises a network analyzer 8 connected to the feed antenna 1, which is configured, on the one hand, to apply the measurement signal to the feed antenna 1 so that it is emitted by the feed antenna 1, and, on the other hand, to receive a portion of the measurement signal reflected back from the feed antenna 1 or a measurement signal derived therefrom so that it can be evaluated in the network analyzer 8. As can be seen in particular from Fig. 4, the network analyzer 8 has an evaluation device 9 configured to determine the transfer function from the feed antenna 1 to the retroreflector 7. In addition, the network analyzer 8 is provided with a time gating device 10 configured to differentiate between signals received by the network analyzer 8 with regard to their propagation time.The procedure used is described in detail below.

[0049] Furthermore, the network analyzer 8 has an input 23 for receiving the reflected measurement signal received from the feed antenna 1 and an output 24 for transmitting the measurement signal to the feed antenna 1. To enable the evaluation of even small signals, an amplifier 11 is connected upstream of the input 23. Furthermore, the arrangement is provided with a transmit frequency converter 12 for applying the measurement signal to the feed antenna 1 to be transmitted, and a receive frequency converter 13 for receiving the reflected portion of the measurement signal. It is essential that the transmit frequency converter 12 and the receive frequency converter 13 of the radar target simulator 6, with which the radar sensor 5 to be tested is to be tested, are used as the transmit frequency converter 12 and the receive frequency converter 13.This has the advantage that the signal does not have to be evaluated in the frequency range up to 81 GHz, which is otherwise common in the automotive sector and would only be possible with very expensive measuring instruments. Instead, the method proposed here allows the use of a network analyzer 8 for frequencies below 6 GHz. Instead of a large laboratory device, a mobile measuring instrument can be used. The required frequency conversion of the measurement signal to the higher frequency is performed by the transmit frequency converter 12, and the conversion of the measurement signal to the lower frequency is performed by the receive frequency converter 13.

[0050] As for the further design of the arrangement, a coupler 14 is connected between the feed antenna 1 on the one hand and the transmit frequency converter 12 and the receive frequency converter 13 on the other hand. This coupler is designed to separate the received radar signal from the transmitted measurement signal. Furthermore, a bandpass filter 15 is connected between the transmit frequency converter 12 and the coupler 14. This bandpass filter is designed such that only radar signals within a predetermined frequency range can be transmitted with the feed antenna 1. In this way, the interference of signals from outside the frequency band on the receive side during downmixing with the desired signals is significantly reduced.In addition, an isolator 16 is connected between the transmit frequency converter 12 and the bandpass filter 15 to attenuate reflected signals coming from the direction of the bandpass filter 15 and the coupler 14 and prevent them from being passed back to the transmit frequency converter 12. This reduces unwanted resonance phenomena caused by reflected signals, which could otherwise reduce the power of the transmitted measurement signal.

[0051] The central control of the arrangement described here is carried out via a PC 22, which is connected via a switch 21 to a positioning controller 20 for the retroreflector 7 installed on the robot arm 17, to the radar target simulator 6, and to the network analyzer 8. In this context, it should be noted again that the illustration in Fig. 3 is purely schematic. In particular, the transmit frequency converter 12 and the receive frequency converter 13, although shown separately from the radar target simulator 6, are nevertheless components of the radar target simulator 6. As previously described, this represents an essential aspect of the presently described preferred embodiment of the invention.

[0052] Furthermore, according to a preferred embodiment of the invention, the sequence shown in Fig. 5 for operating the previously described arrangement is as follows: In a first step S1, the measurement signal is transmitted in the radar frequency range from the feed antenna 1 via the reflector 2 into the radar sensor test zone 3. Subsequently, in step S2, a portion of the measurement signal transmitted into the radar sensor test zone 3 is reflected back via the reflector 2 to the feed antenna 1 by means of the retroreflector 7 arranged in the radar sensor test zone 3. However, it cannot be ruled out that a reflection may occur when the measurement signal is coupled into the feed antenna 1, which would then naturally overlap with the reflected measurement signal. The reflected signal and the reflected measurement signal would then also lie in the same frequency range and therefore could not be separated by a filter.In this respect, the method described here provides that the part of the measurement signal received due to the back reflection from the feed antenna 1 and a reflection signal generated when the measurement signal is coupled into the feed antenna 1 are separated by windowing in the time domain.

[0053] For this purpose, in step S3, the frequency domain data of the received part of the measurement signal and the frequency domain data of the reflection signal created when the measurement signal was coupled into the feed antenna 1 are transformed from the frequency domain to the time domain in a time gating device 10 by means of inverse Fourier transformation. Then, in step S4, a predetermined time range is selected which, on the one hand, contains the time composed of the expected propagation time of the measurement signal on the route from the feed antenna 1 via the reflector 2 to the retroreflector 7 and back, as well as the propagation time of the measurement signal from the feed antenna 1 to the time gating device 10, and which, on the other hand, does not contain the expected propagation time of the reflection signal from the feed antenna 1 to the time gating device 10, so that a windowed time signal is obtained.Finally, in step S5, the windowed time signal is transformed back from the time domain to the frequency domain. The resulting signal then contains the information about the desired transfer function without reflection interference. The transfer function, in turn, is then used, as described above, to correct the alignment of the components feed antenna 1, reflector 2, and radar sensor 5 during test operation.

[0054] List of reference symbols

[0055] 1 feed antenna

[0056] 2 reflectors

[0057] 3 Radar sensor test zone

[0058] 4 absorber chamber

[0059] 5 Radar sensor

[0060] 6 Radar target simulator

[0061] 7 Retroreflector

[0062] 8 Network Analyzer

[0063] 9 Evaluation device

[0064] 10 Time-gating device

[0065] 11 amplifiers

[0066] 12 transmit frequency converters

[0067] 13 Receive frequency converter

[0068] 14 couplers

[0069] 15 bandpass filters

[0070] 16 Insulator

[0071] 17 Robot arm

[0072] 18 Positioning system

[0073] 19 additional components

[0074] 20 Positioning control

[0075] 21 Switch

[0076] 22 PC

[0077] 23 Input of the network analyzer

[0078] 24 Network analyzer output

Claims

Patent claims 1. Arrangement for measuring the transfer function on a path from a feed antenna (1) via a reflector (2) to a radar sensor test zone (3), comprising an absorber chamber (4), wherein the feed antenna (1) is designed to transmit and receive a radar signal and is arranged together with the reflector (2) within the absorber chamber (4), and the radar sensor test zone (3) is a predetermined area within the absorber chamber (4) in which a radar sensor (5) to be tested is to be tested by means of a radar signal transmitted by the feed antenna (1) with the aid of a radar target simulator (6), characterized in that a retroreflector (7) is arranged in the radar sensor test zone (3) in order to reflect at least part of a measurement signal in the radar frequency range received by the feed antenna (1) via the reflector (2) back to the feed antenna (1) via the reflector (2).

2. Arrangement according to claim 1, wherein the arrangement has a network analyzer (8) connected to the feed antenna (1), which is configured, on the one hand, to apply the measurement signal to the feed antenna (1) so that it is emitted by the feed antenna (1), and, on the other hand, to receive a part of the measurement signal reflected back from the feed antenna (1), so that this or a signal derived therefrom can be evaluated in the network analyzer (8).

3. Arrangement according to claim 2, with an evaluation device (9) which is designed to determine the transfer function from the feed antenna (1) to the retroreflector (7).

4. Arrangement according to claim 3, comprising a time gating device (10) which is designed so that signals received by the network analyzer (8) can be differentiated with regard to their propagation time.

5. Arrangement according to one of claims 2 to 4, wherein the network analyzer (8) is provided with an input (23) for receiving the reflected portion of the measurement signal received by the feed antenna (1), which input is preceded by an amplifier (11).

6. Arrangement according to one of the preceding claims, wherein the arrangement comprises a transmit frequency converter (12) for applying the measurement signal to be transmitted to the feed antenna (1) and a receive frequency converter (13) for receiving the reflected part of the measurement signal.

7. Arrangement according to claim 6, wherein the transmit frequency converter (12) is designed for conversion to a higher frequency and the receive frequency converter (13) is designed for conversion to a lower frequency.

8. Arrangement according to claim 6 or 7, wherein a transmit frequency converter (12) and a receive frequency converter (13) of the radar target simulator (6) are used as the transmit frequency converter (12) and as the receive frequency converter (13), with which the radar sensor (5) to be tested is to be tested.

9. Arrangement according to one of the preceding claims, wherein a coupler (14) is connected between the feed antenna (1) on the one hand and the transmit frequency converter (12) and the receive frequency converter (13) on the other hand, which coupler is designed to separate the received measurement signal from the transmitted measurement signal.

10. Arrangement according to claim 9, wherein a bandpass filter (15) is connected between the transmit frequency converter (12) and the coupler (14), which bandpass filter is configured such that only measurement signals lying within a predetermined frequency range can be transmitted with the feed antenna (1).

11. Arrangement according to claim 10, wherein an isolator (16) is connected between the transmit frequency converter (12) and the bandpass filter (15) in order to le coming from the direction of the bandpass filter (15) and the coupler (14) and not to direct them back to the transmit frequency converter (12).

12. Arrangement according to one of the preceding claims, wherein the retroreflector (7) is attached to a movable robot arm (17).

13. Method for measuring the transfer function on a path from a feed antenna (1) via a reflector (2) to a radar sensor test zone (3) in an anechoic chamber (4), comprising the following steps: Emitting a measurement signal in the radar frequency range from the feed antenna (1) via the reflector (2) into the radar sensor test zone (3), Reflecting at least part of the measurement signal emitted into the radar sensor test zone (3) back via the reflector (2) to the feed antenna (1) by means of a retroreflector (7) arranged in the radar sensor test zone (3).

14. The method according to claim 13, wherein the part of the measurement signal received due to the back reflection from the feed antenna (1) and a reflection signal created when the measurement signal is coupled into the feed antenna (1) are separated by windowing in the time domain.

15. Method according to claim 14, comprising the following method steps: Transforming the frequency domain data of the received part of the measurement signal and the frequency domain data of the reflection signal generated when the measurement signal is coupled into the feed antenna (1) by means of inverse Fourier transformation from the frequency domain to the time domain in a time gating device (10), Selecting a predetermined time range which, on the one hand, contains the time composed of the expected propagation time of the measurement signal on the route from the feed antenna (1) via the reflector (2) to the retroreflector (7) and back as well as the propagation time of the measurement signal from the feed antenna (1) to the time gating device (10), and which, on the other hand, does not contain the expected propagation time of the reflection signal from the feed antenna (1) to the time gating device (10), so that a windowed time signal is obtained, and Transforming the windowed time signal from the time domain back to the frequency domain.