Multi-target radar simulator system

Abstract

A system (100) for testing a vehicle radar is described. The system (100) includes a diffractive optical element (104) (DOE (104)) configured to diffract electromagnetic waves incident on a first side (103) from a radar device under test (DUT). The system (100) also includes a re-illumination element adapted to receive the electromagnetic waves diffracted from the DOE (104) from a second side (105). The re-illumination element is adapted to transmit electromagnetic waves with an apparent angle of arrival (AoA) back to the DOE (104).

Description

Background Art

[0001] Millimeter waves are generated by oscillations at frequencies in the spectrum between 30 gigahertz (GHz) and 300 gigahertz. Millimeter wave (mmWave) automotive radar is a key technology for existing advanced driver assistance systems (ADAS) and planned autonomous driving systems. For example, millimeter wave automotive radar is used in advanced driver assistance systems to warn of front and rear collisions. In addition, millimeter wave automotive radar can be used in planned autonomous driving systems to implement adaptive cruise control and autonomous parking, and ultimately for autonomous driving on streets and highways. The advantage of millimeter wave automotive radar over other sensor systems is that it can operate in most types of weather and can operate in both light and darkness. The adaptability of millimeter wave automotive radar reduces costs to the extent that millimeter wave automotive radar can now be deployed in large quantities. As a result, millimeter wave automotive radar is now widely used for long-range, medium-range, and short-range environmental sensing in advanced driver assistance systems. In addition, millimeter wave automotive radar has the potential to be widely used in autonomous driving systems currently under development.

[0002] Real-world driving environments in which automotive radars may be deployed can vary significantly, and many of these environments can be complex. For example, real-world driving environments may contain numerous objects, and some objects encountered in real-world driving environments have complex reflection and diffraction characteristics that affect the return signal. The direct consequence of not correctly sensing and / or interpreting the return signal can be the triggering of erroneous warnings or inappropriate reactions, or the failure to trigger a warning or reaction that should have been triggered, which can lead to an accident.

[0003] Therefore, automakers and automotive radar manufacturers are eager to electronically simulate driving conditions to provide automotive radar systems with the best and most accurate performance.

[0004] Single-target radar simulators are known. However, simulating realistic driving scenarios requires simulating multiple targets. For example, a radar-equipped vehicle might have a car ahead of it in the same lane, a truck ahead of it, a cyclist in a lane to the left, and another car attempting to run a red light at an intersection. Simulating the apparent angle of arrival (AoA) using known devices is slow due to expensive electronics and cannot be scaled to larger values. Furthermore, most known simulators only simulate an incomplete subset of range, speed, and AoA.

[0005] Therefore, there is a need for a system for simulating multiple targets encountered by a radar system that overcomes at least the above-mentioned shortcomings of known radar simulators. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The exemplary embodiments are best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that the various features are not necessarily drawn to scale. In fact, for the sake of clarity of discussion, dimensions may be arbitrarily increased or decreased. Where applicable and practicable, the same reference numerals refer to the same elements.

[0007] FIG1 is a simplified block diagram illustrating a system for testing a vehicle radar, according to a representative embodiment.

[0008] 2 is a simplified diagram of certain components of a system for testing vehicle radar, according to a representative embodiment.

[0009] 3 is a perspective view of a diffractive optical element (DOE) according to a representative embodiment.

[0010] 4 is a simplified circuit diagram of a modulated reflective device (MRD) according to a representative embodiment.

[0011] 5A is a graph of frequency versus time of a chirp signal, according to a representative embodiment.

[0012] 5B is a graph of frequency versus time of a chirp signal, according to a representative embodiment.

[0013] 6A is a simplified schematic diagram of a re-illuminator according to a representative embodiment.

[0014] 6B illustrates the phase relationship of the in-phase and quadrature components of the mixers of the MRD of FIG. 6A , according to a representative embodiment.

[0015] 7 is a simplified diagram of certain components of a system for testing a vehicle radar including active echo cancellation, according to a representative embodiment. DETAILED DESCRIPTION

[0016] In the following specific embodiments, for the purpose of explanation and not limitation, representative embodiments of the disclosure details are set forth to provide a thorough understanding of the embodiments according to the present teachings. The description of known systems, equipment, materials, operating methods and manufacturing methods can be omitted to avoid blurring the description of the representative embodiments. Nevertheless, systems, equipment, materials and methods within the knowledge of those of ordinary skill in the art are also within the scope of the present teachings and can be used according to the representative embodiments. It should be understood that the terms used herein are only used to describe specific embodiments and are not intended to be restrictive. The defined terms are supplements to the technical and scientific meanings of the defined terms that are generally understood and accepted in the technical field of the present teachings.

[0017] It should be understood that although the terms first, second, third, etc. can be used to describe various elements or components herein, these elements or components should not be limited by these terms. These terms are only used to distinguish one element or component from another element or component. Therefore, without departing from the teachings of this disclosure, the first element or component discussed below can be referred to as the second element or component.

[0018] The terms used herein are used only to describe specific embodiments and are not intended to be limiting. As used in the specification and the appended claims, the singular forms of the terms "a," "an," and "the" are intended to include both the singular and the plural, unless the context clearly dictates otherwise. In addition, when used in this specification, the terms "comprises" and / or "comprising" and / or similar terms clarify the presence of the features, elements, and / or parts, but do not exclude the presence or addition of one or more other features, elements, parts, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0019] Unless otherwise specified, when an element or component is referred to as being “connected to” or “coupled to” another element or component, it should be understood that the element or component can be directly connected or coupled to the other element or component, or that intervening elements or components may be present. In other words, these and similar terms cover situations where one or more intermediate elements or components may be used to connect two elements or components. However, when an element or component is referred to as being “directly connected to” another element or component, this only covers situations where the two elements or components are connected to each other without any intermediate or intervening elements or components.

[0020] As described herein in conjunction with various representative embodiments, a system for testing a vehicle radar is disclosed. The system includes a diffractive optical element (DOE) configured to diffract electromagnetic waves incident on a first side from a radar device under test (DUT). The system also includes a re-irradiation element adapted to receive electromagnetic waves diffracted from the DOE from a second side. The re-irradiation element is adapted to transmit electromagnetic waves with an apparent angle of arrival (AoA) back to the DOE. The system also includes a controller comprising a memory for storing instructions and a processor for executing the instructions. The controller controls the re-irradiation element and is configured to perform performance testing on a vehicle radar including multiple targets.

[0021] FIG1 is a simplified block diagram illustrating a system 100 for testing a vehicle radar according to a representative embodiment. As will be appreciated by those skilled in the art having the benefit of this disclosure, one possible vehicle radar is an automotive radar used in various capacities in current and emerging automotive applications. However, it is emphasized that the presently described system 100 for testing a vehicle radar is not limited to automotive radar systems, but can be applied to other types of vehicles, including buses, motorcycles, electric bicycles (e.g., scooters), and other vehicles that can employ a vehicle radar system.

[0022] According to a representative embodiment, system 100 is arranged to test a radar device under test (DUT) 102 and includes a diffractive optical element 104 and a plurality of re-illuminators 106. Each re-illuminator 106 includes an antenna 108 and an MRD 110. As described more fully herein, there is one re-illuminator for each simulated target.

[0023] The system also includes a computer 112. The computer 112 illustratively includes a controller 114 described herein. The controller 114 described herein may include a memory 116 for storing instructions and a processor 118 for executing instructions to implement the processes described herein. The controller 114 may be housed within a workstation or linked to a workstation, such as another component of the computer 112 or one or more computing devices, a display / monitor, and one or more input devices (e.g., a keyboard, a joystick, and a mouse), in the form of a standalone computing system, a client computer of a server system, a desktop, or a tablet computer. The term "controller" broadly encompasses all structural configurations of a dedicated motherboard or dedicated integrated circuit for controlling the various principle applications described in this disclosure, as understood in the art of this disclosure and as exemplarily described in this disclosure. The structural configuration of a controller may include, but is not limited to, one or more processors, one or more computer-usable / computer-readable storage media, an operating system, one or more application modules, one or more peripheral device controllers, one or more slots, and one or more ports.

[0024] In addition, although the computer 112 is shown as networked components, two such components can be integrated into a single system. For example, the computer 112 can be integrated with a display (not shown) and / or with the system 100. That is, in some embodiments, the functions attributed to the computer 112 can be implemented (e.g., performed) by the system 100 including the first medical imaging system 410. On the other hand, the networked components of the computer 112 can also be spatially distributed, such as by being distributed in different rooms or different buildings, in which case the networked components can be connected via a data connection. In yet another embodiment, one or more components of the computer 112 are not connected to other components via a data connection, but are manually provided with input or output, such as by a memory stick or other form of memory. In yet another embodiment, the functions described herein can be performed based on the functions of the components of the computer 112 but outside the system 100.

[0025] Although the various components of system 100 are described in greater detail in conjunction with the representative embodiments below, a brief description of the functionality of system 100 is currently presented.

[0026] In operation, radar DUT 102 emits a signal (illustratively, a mmWave signal) that is incident on first side 103 of DOE 104. As described more fully herein, the signal from radar DUT 102 is diffracted by DOE 104 and focused at a corresponding one of antennas 108, which are advantageously relatively high-gain antennas, as described more fully below. Thus, DOE 104 diffracts the incident wave at a specific angle relative to second side 105, and each diffracted wave is focused at a corresponding one of antennas 108. In particular, the corresponding focus point (alternatively, focal point) at each of antennas 108 represents a target simulated by system 100.

[0027] Again, each signal diffracted by the DOE 104 is incident on a corresponding one of the antennas 108 of the re-illuminator 106. The signal incident on the antenna 108 is provided to a corresponding one of the MRDs 110. As described more fully herein, frequency modulation of the incident signal is implemented in each MRD based on input from the controller and beneficially simulates the distance of the target from the radar DUT 102, or the velocity of the target relative to the radar DUT 102, or both. In addition, and again as described more fully herein, the azimuth angle (in the coordinate system of FIG. 1 ) is + x direction) and elevation angle (in the coordinate system of Figure 1 + z-direction) is simulated by antenna 108, which is illustratively mechanically gimbaled, or a combination of mechanical gimbaling and electronic simulation.

[0028] The re-illuminated signal is incident on the second side 105 of the DOE 104 and is diffracted again and is incident on the radar DUT 102. The computer 112 receives the signal from the radar DUT 102 for further analysis of the accuracy of the radar DUT 102.

[0029] 2 is a simplified diagram of certain components of a system 200 for testing vehicle radar according to a representative embodiment. Aspects of system 100 described in conjunction with the representative embodiment of FIG1 may be common to the presently described system 200 and, although, may not be repeated.

[0030] System 200 is configured to test radar DUT 202 and includes DOE 204 , first re-irradiation antenna 206 , second re-irradiation antenna 208 , third re-irradiation antenna 210 , and fourth re-irradiation antenna 212 .

[0031] Each of the first through fourth re-irradiation antennas 206 through 212 is connected to delay electronics 214 , which includes at least one MRD (not shown in FIG. 2 ) and is described more fully below.

[0032] 3 , DOE 204 is a generalization of a Fresnel lens in which the diffractive elements have dimensions selected to diffract electromagnetic radiation of a desired frequency range. As described above, the radar signal of the radar DUT of the present teachings is in the millimeter wave range.

[0033] DOE 204 has a single focal point 216 (alternatively, a single "focal point") on side 219, on DOE axis 217 and at radar DUT 202; and multiple focal points (alternatively, multiple focal points, or multiple focal points) on the side opposite side 217, facing the first through fourth re-irradiation antennas 206 through 212. Each of these multiple focal points is located at the input of one of the first through fourth re-irradiation antennas 206 through 212. Typically, the number of multiple focal points on the side opposite side 219 is selected to maximize the number of possible targets. In certain representative embodiments, DOE 204 focuses the signal from the radar DUT at ten or more locations. Simulating the signal from the radar DUT 202 requires placement of appropriate receiving devices (e.g., a horn selected for the radar DUT signal frequency and acting as a receiver) at the locations where the signal from DOE 204 is focused. Specifically, the number of simulated targets is controlled by selecting the number of re-irradiation antennas or the number of active re-irradiation antennas. As such, although the radar signal emitted from the single focal point 216 at the radar DUT 202 is diffracted to a plurality of focal points on the side opposite to the side 219 , target simulation may not be performed on each diffracted signal.

[0034] According to a representative embodiment, each of the first through fourth re-irradiation antennas 206 through 212 is a relatively high-gain antenna having a gain of at least approximately 20 dBi. Specifically, the first through fourth re-irradiation antennas 206 through 212 are not dipole horns or low-gain horns, as such devices may re-irradiate excessively (if not entirely) the DOE 204, resulting in errors in the AoA of the simulated target. Instead, in certain representative embodiments, it is contemplated that the first through fourth re-irradiation antennas 206 through 212 are point-focus antennas. Illustratively, the focal length of a point-focus antenna is between approximately 30% and approximately 100% of the distance between the focal point at the particular point-focus antenna and the DOE 204. The spot size illustratively has a diameter in the range of approximately 1 cm to approximately 6 cm.

[0035] In operation, a radar signal is incident on DOE 204 from a single focal point 216 of radar DUT 202 and is diffracted by DOE 204. The single radar signal transmitted from radar DUT 202 is incident on side 219 and, after diffraction, emerges from the side of DOE 204 opposite side 219 as multiple radar signals. Each of these multiple radar signals is diffracted by DOE 204 and focused on one of the first to fourth re-illumination antennas 206 to 212. The radar signals incident on the first to fourth re-illumination antennas 206 to 212 are input to delay electronics, which simulate the target range and relative velocity between the target and radar DUT 202.

[0036] In certain exemplary embodiments, the azimuth (position relative to DOE axis 217 along the x-direction of the coordinate system of FIG. 2 ) and elevation (position relative to DOE axis 217 along the y-direction of the coordinate system of FIG. 2 ) of the simulated signal from each target are simulated by mechanically gimbaling (as indicated by the arrows) the first through fourth re-illumination antennas 206 through 212. In other exemplary embodiments described herein, components of the delay electronics disclosed herein are used to electronically implement one of the azimuth or elevation orientations (i.e., angular orientations) of the re-illumination radar signals from the first through fourth re-illumination antennas 206 through 212 to the side of DOE 204 opposite side 219. Thus, in certain exemplary embodiments, a combination of mechanical gimbaling and electronic beamforming of the first through fourth re-illumination antennas 206 through 212 is used to determine a sub-region of the side of the DOE opposite side 219, and ultimately determine the simulated position and orientation of the target. Stated slightly differently, according to certain representative embodiments, simulation of the AoA degrees of freedom (azimuth and elevation) can be performed in a fully mechanical manner without electronic control; or mechanical for one AoA degree of freedom (e.g., apparent elevation) and electronic for another AoA degree of freedom (e.g., apparent azimuth).

[0037] According to certain representative embodiments, the first through fourth re-illumination antennas 206 through 212 are relatively high-gain antennas and, as described above, can be so-called point-focused antennas (such as lens horns). Thus, the first through fourth re-illumination antennas 206 through 212 of the depicted embodiment receive radar signals diffracted to multiple focal points at respective locations of the inputs of the first through fourth re-illumination antennas 206 through 212 and re-illumination four (again, more or fewer depending on the desired number of targets) relatively small sub-areas of the DOE 204. The re-illumination millimeter-wave DOE 204 presents the apparent azimuth and elevation angles of the sub-area points relative to the normal of the radar DUT 202, and thus provides a simulated AoA of the simulated target. These re-illumination radar signals are then received by the radar DUT 202, and the accuracy of the radar DUT 202 is determined using a computer (e.g., computer 112).

[0038] As shown in FIG2 , there are four regions O1, O2, O3, and O4 where radar signals from the first to fourth re-illumination antennas 206 to 212 are incident on the DOE 204. Each of these four regions is focused on a single focal point 216 at the radar DUT 202. These four regions are simulated AoA target sub-regions and represent the AoAs of four (in this case) simulated targets. In particular, the optional beam expansion lens 220 may be provided, resulting in a relatively wide azimuth angle presented by the first target at O1 on the side 219 of the DOE 204.

[0039] Four (in this illustration) regions O1, O2, O3, and O4 are target points illuminated by the illustrative gimbaled first through fourth re-illumination antennas 206 through 212 (which may be point-focus antennas). DOE 204 can be considered somewhat "angle-independent" toward radar DUT 202, but the entire DOE (including regions not illuminated by the first through fourth re-illumination antennas 206 through 212 at a given point in time) is designed to separate its focus to each of the first through fourth re-illumination antennas 206 through 212. At another moment in time, one or more of the first through fourth re-illumination antennas 206 through 212 may be gimbaled to a different point on DOE 204, such that another region (e.g., O5 (not shown)) will be the new apparent angle target. Thus, the reorientation of the first through fourth re-illumination antennas 206 through 212 (again, in this illustration) presents a "new" apparent target for simulation system 200.

[0040] As will be appreciated, simulation of the azimuth and elevation angles of the target is achieved using the diffraction characteristics of the DOE 204, the orientations of the first through fourth re-illumination antennas 206 through 212, and, in some cases, a beam-shaping lens selected for a specific wavelength (e.g., millimeters) of the signal from the radar DUT 202. Through the present teachings, the distance between the radar DUT 202 and the target, or the relative velocity of the radar DUT 202 and the target, or both, is electronically simulated using an MRD.

[0041] FIG3 is a perspective view of a DOE tile 300 according to a representative embodiment.

[0042] Similar to DOE 204, DOE tile 300 is a generalization of a Fresnel lens, where the diffractive elements have dimensions selected to diffract electromagnetic radiation of a desired frequency range.As described above, the radar signal of the radar DUT of the present teachings is in the millimeter wave range.

[0043] The DOE tile 300 is transparent to the wavelength of the radar DUT (e.g., millimeter waves) and is made of a suitable material for such transparency. Illustratively, the DOE tile 300 can be made of a suitable polymer that has been processed to include a gradient as depicted in FIG. 3 , such as polystyrene, acrylic, polycarbonate, Ultem, or rexolite. Additionally, as shown in FIG. 3 , the DOE tile 300 has a gradient formed thereon to provide diffraction of electromagnetic radiation incident thereon. The gradient has a suitably selected size to provide a piecewise linear approximation to a smoothly curved lens. In an illustrative embodiment in which the DOE tile 300 is made of plastic or a similar material, the gradient is provided by processing a substrate of a selected material to have a desired gradient profile. According to a representative embodiment, a plurality of DOE tiles 300 can be used to provide a DOE (e.g., DOE 204). For example, one (1) to eight (8) DOE tiles 300 can be used to provide a DOE.

[0044] As described above, the DOE tile 300 has a first side that provides a single focal point and is located closest to the radar DUT, and a second side that provides multiple focal points, opposite the first side and located closest to the re-illumination antenna. The number of focal points is selected to provide the maximum number of targets to be simulated. However, as described above, not all targets need to be simulated, so the number of targets being simulated in a particular test is based on the number of active re-illumination antennas.

[0045] As described above, the apparent or simulated distance to radar DUT 202 is determined by providing a delay in the signals received by the corresponding first to fourth re-illumination antennas 206 to 212. If the first to fourth re-illumination antennas 206 to 212 were connected to a reflective open circuit or open circuit, the apparent target distance would be the ray-traced distance (plus a small correction due to lens delay, antenna delay, etc.). In this way, the apparent target distance is simply the sum of the DUT sub-area distance plus the sub-area to re-illumination distance. Furthermore, in this scenario, there would be no relative velocity between radar DUT 202 and the target. Therefore, in FIG2 , the apparent or simulated distance between radar DUT 202 and target 2 is simply the ray-traced distance from radar DUT 202 to sub-area O2 plus the distance from O2 to the second re-illumination antenna 208. However, most driving simulation tests require simulation distances on the order of approximately 1 meter to approximately 100 meters. Additionally, the direction of the target is determined by the system 200 and, when combined with the simulated relative velocity between the radar DUT 202 and the target being simulated, provides a simulation of the relative velocity of the target being simulated.

[0046] As described above, simulation of distance and velocity is performed by connecting each of the first through fourth re-irradiation antennas 206 through 212 to the MRD, and a representative embodiment will now be described in conjunction with FIG. 4 .

[0047] Figure 4 is a simplified circuit diagram of a modulated reflective device (MRD) 400 according to a representative embodiment. Aspects of the MRD 400 described in conjunction with the representative embodiment of Figure 4 may be common to the MRDs and delay electronics described above, although they may not be repeated.

[0048] The MRD 400 is connected to a re-irradiation antenna 401 and can therefore be one of the re-irradiation antennas described above. Of course, in practice, there may be more than one MRD 400 in the system, and therefore more than one re-irradiation antenna 401 (e.g., as depicted in the representative embodiment of FIG2 ). In certain representative embodiments, the re-irradiation antenna 401 is a horn selected for the wavelength of the signal received from the radar DUT (not shown in FIG4 ). The re-irradiation antenna 401 can have variable gain and can be coupled to a beam shaping element (such as a lens) to adjust the degree of freedom of the AoA, as described above. It is not necessary to use a horn or similar antenna for the re-irradiation antenna 401, and other types of antennas are contemplated, such as a patch antenna or a patch antenna array (described below).

[0049] MRD 400 includes a circulator 402 connected to a mixer 403. Mixer 403 is an in-phase (I) and quadrature (Q) mixer (IQ mixer). For reasons described below, the mixer can advantageously be a single-sideband (IQ) mixer with standard 90° phasing of the RF signal, resulting in an output of either the upper sideband (USB) or the lower sideband (LSB), thereby rejecting the LSB or USB, respectively. The output of mixer 403 is provided to a variable gain amplifier (VGA) 404, which includes a gain control input 405. As described above, the gain control input 405 of VGA 404 is connected to a computer (e.g., computer 112 of FIG. 1 ). In particular, VGA 404 enables appropriate simulation of the re-illumination signal received from the DOE at the re-illumination antenna 401. Specifically, as described above, the incident signal from the radar DUT on the DOE is split between multiple focal points at the re-illumination antenna 401. In this way, once diffracted by the DOE, the power of the signal is split, and thus the power of each radar signal diffracted to the multiple focal points at re-illumination antenna 401 is reduced compared to the output power of the radar signal from the radar DUT. Furthermore, as described above, the portion of the signal diffracted from the focal points on the side of the DOE facing re-illumination antenna 401 (and therefore the power) depends on the orientation of re-illumination antenna 401 relative to the focal point or focal points at re-illumination antenna 401. Thus, the power of the signal incident on re-illumination antenna 401 may be insufficient to be retransmitted back to the radar DUT and thus used for accurate testing. Furthermore, the power of the re-illumination signal from re-illumination antenna 401 is an indicator of the simulated distance between the target and the radar DUT. Thus, the gain provided by VGA 404 is selected at gain control input 405 based on the power of the radar signal incident on re-illumination antenna 401 and the desired simulated distance of the target being simulated.

[0050] In particular, power is used to simulate a consistent radar cross section (RCS). The radar cross section (RCS) can be stored in a lookup table. To do this, for a given range r, it is known that the return signal is proportional to the RCS and falls off as 1 / r. 4 A vehicle is typically considered to be 10dBsm, which is radar parlance for measuring area, meaning 10dB relative to one square meter (sm), or simply, 10 square meters. Many objects have been tabulated (people, cyclists, buildings, etc.), and those that have not can now be calculated using ray tracing techniques. Throughout this teaching, the focus is on providing the radar DUT with a radar signal at a distance r (following the well-known 1 / r 4The return signal strength is commensurate with the radar attenuation law and the acceptable RCS value for a particular object. According to representative embodiments, the signal strength (and therefore power) is adjusted by adjusting the strength of the I / Q drive signals from the computer 112 to the MRD of each embodiment, where a weaker I / Q drive signal provides a relatively weaker simulated signal. In particular, in certain representative embodiments, the computer 112 pre-calculates a consistent return signal for a single focal point at the radar DUT, and the controller 114 then adjusts the strength of the I and Q drives to achieve this SSB strength. Alternatively, and advantageously, the gain of the VGA 404 can be adjusted to control the return SSB strength.

[0051] Because many vehicle radars are frequency modulated continuous wave (FMCW) devices, there is no need to implement a true variable delay line to emulate a variable apparent time delay. Instead, the range / speed is emulated electronically using the MRD 400. To do this, FMCW radar systems use a chirped waveform whereby the correlation of the original transmit (Tx) waveform from the radar DUT with the receive (Rx) echo waveform reveals the target range. For example, at a chirp rate of ±k SW In an upchirp / downchirp system (measured in Hz / second), a target at distance d and zero relative velocity with respect to the host vehicle will cause a frequency shift (δf) given by:

[0052] δf=–(±2k SW d / c) (Equation (1))

[0053] Where c is the speed of light, and the factor of 2 is due to the round-trip propagation of the signal from the radar DUT. The sign of the shift depends on which part of the waveform is being processed (upchirp vs. downchirp). In contrast, the Doppler shift due to relative velocity appears as a "common-mode" frequency shift; for example, a net upshift on both halves of the waveform indicates that the radar DUT is approaching the target. Correlation is performed in the DUT's IF / baseband processor; bandwidths of several MHz are typical.

[0054] The most commonly deployed FMCW variations use either repetitive upchirps or repetitive downchirps, but not both (with an intervening dead time). Thus, the range to the target is determined as in the previous paragraph, now without the sign issue. Relative velocity is determined by measuring the phase shift between successive frame IF correlation signals, where a frame is a term for one period of the waveform. In many FMCW radar applications, the frame repetition rate is typically several kHz.

[0055] A known method introduces the concept of receiving the transmitted signal from the radar DUT at one or more probe points and then applying balanced phase modulation to the received signal before returning the signal to the radar DUT. Because phase modulation is another form of frequency modulation, the balanced phase modulation of this known system causes double-sideband (DSB) modulation of the original signal, thereby suppressing the original swept carrier. Balanced phase modulation is relatively easy to implement because one can simply switch between turning on an open load and a short load. If the modulation frequency is δf*, and the time-correlated frequency of the original signal is f(t), then due to the relatively slow chirp rate, the time-correlated frequency of the return signal is f(t) ± δf*. From equation (1), by choosing

[0056] δf*=2k SW (d em -d su ) / c (Equation (2))

[0057] The known method cited is for setting the distance d su Simulated target distance d em , the setup distance is the physical distance between the radar DUT and the probe. Unfortunately, due to its DSB modulation, for em,j For each intentionally created target j at a distance d em,j ±2d su,j Create a double image target at d su,j is the setup distance to probe j, where the sign in the “ghosting equation” depends on the sign of the chirp slope.

[0058] For long-range radar (LRR), a range accuracy of 10 cm is desired, while short-range radar (SRR) strives for 2 cm accuracy. This means that the setup distance for a known DSB modulation test setup must be <5 cm for LRR and <1 cm for SRR, with double imaging being irrelevant. Achieving this setup is very difficult because the setup distance includes the actual radar patch antenna-to-bumper distance, the bumper-to-probe distance, and the effective bumper thickness (the actual bumper thickness multiplied by the millimeter-wave refractive index of the bumper material).

[0059] Another drawback of known DSB modulation test setups is the inability to simulate variable AoA. In such known systems, the apparent AoA is fixed. In principle, the AoA could be varied by mounting the probe on a translation stage, but this would then encounter the obstruction issues mentioned in the introduction. Of course, this is not very efficient.

[0060] A third disadvantage of the referenced known systems is that the dynamic range of the radar cross section (RCS) (i.e., the strength of the echo) is limited to less than 20 dB. This is because there is no matching load state for the switches used in known systems, only a crossover point between "open circuit" and "short circuit" that acts as a quasi-match when the modulation is switched off and the switch is biased at that point. Replacing the three-state switch is not an adequate solution to increase the dynamic range because the RCS must vary almost continuously. Automotive radar RCS needs to vary between 25 dB and 50 dB, depending on various estimates.

[0061] Referring again to FIG. 4 , once amplified / attenuated at circulator 402 , the MRD provides an amplified / attenuated SSB signal that is returned to circulator 402 and retransmitted out to re-illumination antenna 401 .

[0062] Specifically, in the representative embodiment of the SSB MRD 400, reducing the strength of the modulated I and Q drive signals will reduce the output tone intensity and, therefore, the RCS. In practice, this approach likely cannot achieve more than 15dB to 20dB of dynamic range using modulated drive alone. However, the VGA 404 compensates for the lack of achieving the desired RCS dynamic range, and variable gain of 10dB to 50dB can be easily achieved through a combination of a variable attenuator and amplifier bias adjustment. Simulating the relative velocity of a target in a system for testing a vehicle radar according to a representative embodiment requires synchronization between the modulation and the radar DUT frame. This synchronization can be achieved by providing a trigger signal from the radar DUT or deriving such a trigger. The triggering can be facilitated by using an auxiliary detector (sometimes called a "sniffer") or by tapping the output of the circulator 402. For example, the auxiliary detector can be used to detect the arrival of the first and second chirps of each frame of the radar DUT. In an example with a frame rate of approximately 10 fps (frames per second), recording the time interval between only two chirps in a burst or frame allows a consistent chirp repetition rate to be determined for the simulation using equation (3) below. For up-chirp / down-chirp radar DUTS, synchronization governing the switch from LSB to USB is shown in FIG5A . For all up-chirp radars, synchronization allows phase zero to be associated with the start of a frame. Thus, according to a representative embodiment, a phase slip in the modulated signal is introduced between frames that accurately mimics the phase slip that the radar DUT would encounter in the presence of relative velocity, as discussed below in conjunction with FIG5B .

[0063] Referring to FIG5A , a graph of frequency versus time depicts up-chirp / down-chirp according to a representative embodiment. Curve 501 represents the Tx chirp signal from the radar DUT, and curves 502 and 503 represent the re-irradiation signal from the MRD (e.g., MRD 400). During the up-chirp (down-chirp) period, the LSB (USB) signal is selected. In particular, for clarity of description, the gap between curve 501 and curves 502 and 503 is exaggerated; in fact, due to δf u * and δf d * is at most a few MHz, so the gap is relatively small, while the chirp span is typically 1 GHz to 4 GHz. Therefore, for correlation purposes, the gap is negligible. Therefore, curves 502, 503 look like delayed versions of curve 501, where the delay corresponds to the simulated distance between the radar DUT and the specific target. The relative velocity is given by applying a non-positive δf u * and non-negative δf d *The commonly used Doppler formula for the algebraic mean is given by

[0064] Referring to Figure 5B , a graph of frequency versus time depicts upchirp / downchirp according to a representative embodiment. Δφ is the frame-to-frame phase slip intentionally introduced into the modulated signal of the MRD. When received by the DUT Rx, the upchirp / downchirp FMCW DUT processes the frame, detects this phase slip, and perceives the relative velocity. Again, the radar DUT interprets the inferred delay between curves 501 and 502 as target range.

[0065] In particular, there are both coarse and fine velocities. The coarse velocity is simply the distance between frames divided by the change in frame time, typically on the order of 0.1 seconds. The fine velocity (sometimes called Doppler) is calculated by measuring the IF phase slip Δφ between consecutive chirps. If T is the chirp-to-chirp period, and λ is the mid-band wavelength, then

[0066] v 细 =λΔφ / (4πT) (Equation (3))

[0067] Coarse speed typically covers roughly +-5 mph to >+-100 mph. Fine speed is a fine adjustment (Vernier) that can extend the resolution / accuracy to about +-0.1 mph. Fine speed typically runs into aliasing at about 5 mph to 7 mph, but this is when the coarse speed takes over to eliminate aliasing. In particular, coarse and fine speeds can be combined to obtain a continuous speed measurement from a few miles per hour to hundreds of miles per hour with an accuracy and resolution of less than 1 mph.

[0068] In the representative embodiments described thus far, the target's delay and, therefore, range and velocity are simulated electronically, while the target's AoA, azimuth, and elevation degrees of freedom are simulated mechanically (e.g., via gimbaling). The presently described representative embodiments allow for electronic simulation of azimuth as well as range and velocity. In particular, while the presently described representative embodiments are described only in conjunction with electronic azimuth simulation of a target, it should be noted that, in alternative embodiments, elevation can also be simulated.

[0069] Figure 6A is a simplified schematic diagram of a re-illuminator 600 according to a representative embodiment. Aspects of the re-illuminator 600 described in conjunction with the representative embodiment of Figure 6A may be common to the re-illuminators and systems described above, although they may not be repeated.

[0070] First, it should be noted that the re-illuminator 600 may be used for one of the first through fourth re-illuminator antennas 206 through 210, which may be connected to a corresponding one of the MRDs 400. As such, multiple targets being simulated (not shown in FIG. 6A ) would require multiple (active) re-illuminators 600, with each active re-illuminator 600 being implemented to simulate the range / velocity and AoA of each target being simulated.

[0071] Re-illuminator 600 includes a first MRD 601 connected to a first patch antenna array 602, a second MRD 603 connected to a second patch antenna array 604, and so on, and an nth MRD 605 connected to the nth patch antenna array. As described herein, phase delay is introduced from successive MRDs and simulates the azimuth angle of a single target (not shown in FIG6A ).

[0072] According to a representative embodiment, the first, second, and nth patch antenna arrays 602, 604, 606 are so-called microstrip antenna arrays. Each of the first, second, and nth patch antenna arrays 602, 604, 606 includes a plurality of patch antennas connected in series, such as by a suitable signal transmission line, and are therefore substantially in phase with each other.

[0073] To provide azimuth simulation of a target, the electrical phase between adjacent patch antenna arrays is varied to scan in the azimuth direction. Specifically, as shown, each of the first, second, and nth patch antenna arrays 602, 604, 606 is fed by a corresponding one of the first, second, ..., nth MRDs 601, 603, 605, where the phase of each subsequent MRD's output is delayed compared to the previous one. Specifically, the phase and frequency of the chirped input signals to the corresponding first, second, ..., nth MRDs 601, 603, 605 result in phase changes between each successive path antenna array, which determines the control of range and Doppler velocity.

[0074] In particular, the MRD of the present teachings does not require a local oscillator (LO) because the MRD acts as a transponder, rather than a transmitter or receiver requiring LO modulation or demodulation. It should be noted that although many known transponders operate by receiving, downconverting, IF processing, upconverting, and retransmitting, this processing chain is by no means required.

[0075] Relative in-phase phasing and the same relative quadrature-phase phasing at a common modulation frequency δf* are applied to the first, second, ... nth MRDs 601, 603, 605 connected to the same re-illuminator. In particular, "relative" phasing can be understood in the representative embodiment of FIG6A as the δf* phase on the I(Q) channels of successive MRDs connected to the re-illuminator. As shown in FIG6B , each MRD IQ coordinate system is rotated compared to the previous adjacent MRD. Again, it should be noted that δf* is typically only a few MHz, so many phase applications can be implemented with both low loss and low cost. The relative phasing applied to the I and Q modulation channels results in relative phasing of the SSB chirp return signals across the n patch antenna array, thereby achieving azimuth steering through the well-known RF phased array principle.

[0076] Referring again to Figures 6A and 6B, the first patch antenna array 602 can be considered a reference array. The output of the second patch antenna array 604 is rotated when retransmitted, and therefore the I2 of the second patch antenna array 604 is offset relative to the I1 of the first patch antenna array 602. This phase progression continues with successive phased antenna arrays, with an electronic azimuth delay applied to the signal at a halfway point between the radar DUT and the re-illuminator for the particular target being simulated. When retransmitted from the re-illuminator 600, the signal is biased and appears to be from a different point (in azimuth) of the system's DOE. In this way, the re-illuminator 600 allows for simulation of a (single) target in the azimuth direction. Similarly, for each target being simulated in azimuth, one re-illuminator 600 can be implemented for one re-illuminator antenna / MRD as described in conjunction with the systems and components of the representative embodiments of Figures 2 to 4.

[0077] As will be appreciated, specular reflections from one or more of the above-described systems' DOEs can result in an ever-present echo signal from the DOE at the radar DUT. The present teachings contemplate both passive techniques that substantially remove this echo signal and active approaches that substantially remove this echo signal.

[0078] FIG7 is a simplified diagram of certain components of a system 700 for testing a vehicle radar including active echo cancellation according to a representative embodiment. Aspects of the system 700 described in conjunction with the representative embodiments of FIG1 through FIG6B may be common to the presently described system 700 and, although, may not be repeated.

[0079] System 700 is configured to test a radar DUT 702 and includes a DOE 704, a first re-irradiation antenna 706, a second re-irradiation antenna 708, a third re-irradiation antenna 710, and a fourth re-irradiation antenna 712. Each of the first through fourth re-irradiation antennas 706 through 712 is connected to delay electronics 714, which includes at least one MRD (not shown in FIG. 2 ) and is described more fully below.

[0080] 3 , DOE 704 is a generalization of a Fresnel lens in which the diffractive elements have dimensions selected to diffract electromagnetic radiation of a desired frequency range. As described above, the radar signal of the radar DUT of the present teachings is in the millimeter wave range.

[0081] DOE 704 has a single focal point 716 at the location of radar DUT 702 on DOE axis 717, and multiple focal points on the side opposite side 719, one of which is located at a corresponding one of the first to fourth re-irradiation antennas 706 to 712. Generally, the number of focal points on the side opposite side 719 is selected to maximize the number of possible targets. As described above, the present teachings contemplate ten targets, and therefore require that the signal diffracted by DOE 704 be focused at a point located at the input of each re-irradiation antenna (in this case, at each of the first to fourth re-irradiation antennas 706 to 712). Specifically, the number of simulated targets is controlled by selecting the number of re-irradiation antennas or the number of active re-irradiation antennas. Thus, while a radar signal emitted from a single focal point at radar DUT 702 is diffracted and incident on multiple focal points at each of the first to fourth re-irradiation antennas 706 to 712, target simulation need not be performed for each diffracted signal.

[0082] In operation, a radar signal from the radar DUT 702 is transmitted to the DOE 704 at a single focal point 716 located at the radar DUT 702 and is diffracted and mapped to a plurality of focal points at the first to fourth re-illumination antennas 706 to 712 located on a side of the DOE opposite to the side 719. The radar signal is further transmitted to a plurality of focal points at each of the first to fourth re-illumination antennas 706 to 712. The radar signals incident on the first to fourth re-illumination antennas 706 to 712 are input to delay electronics, which simulates the target range and relative velocity between the target and the radar DUT 702.

[0083] One aspect of echo cancellation is achieved using a low dielectric constant lens material applied to side 719. While this reduces the refractive index retardation relative to air, the wavelength from radar DUT 702 is short enough that a few millimeters of stepping is standard, making the overall lens thickness very reasonable. According to another aspect of echo cancellation, in a representative embodiment where the cancellation of the echo from DOE 704 is achieved passively, multiple symmetrical patterns are provided.

[0084] In the presently described embodiment, DOE 704 has four-fold symmetry, i.e., the left and right halves of DOE 704 are mirror images of each other; and the top and bottom halves of DOE 704 are mirror images of each other. The lens axis passes from the center of radar DUT 702 through the center of symmetry of the re-illumination antenna.

[0085] In general, achieving symmetry for DOE 704 greater than 4-fold becomes complex. However, multiples of 4-fold symmetry are relatively easy to establish. Therefore, and again for purposes of illustration and not limitation, the maximum number of targets can be selected to be a multiple of 4 to maintain symmetry, although not all targets must be simulated simultaneously as described herein. Thus, for example, if it is desired to simulate 10 targets, DOE 704 can be designed to simulate 12 targets (thus maintaining 4-fold symmetry), with the two re-illumination antennas associated with the VGAs turned off and therefore not representing the targets.

[0086] Since the focal depth of a lens is never less than a wavelength λ (at least not for any class of lenses contemplated by the present teachings), the DOE 704 is divided into quadrants, and the quadrants are staggered. As is known in the art, staggering is the physical shifting of the DOE tiles in the z-direction of FIG. 7 along the DOE axis 717. In a representative embodiment, the staggering is 0 or λ / 4 in the axial direction without changing the focal characteristics. In the representative embodiment of FIG. 7, the first quadrant 721 and the second quadrant 722 are staggered and each achieves a phase shift of λ / 4 of the reflected signal from the radar DUT 701, where λ is the wavelength of the reflected signal. The third quadrant 723 and the fourth quadrant (but in contrast) are not staggered. In this way, a 2nd order zero in the reflection on the DOE axis 717 is achieved. Again, the first quadrant 721 and the second quadrant 722 are axially staggered by λ / 4. This produces an additional λ / 2 phase shift in the radar signals reflected from the first quadrant 721 and the second quadrant 722 (with no change in transmission amplitude or phase), so the sum of the reflections from the four quadrants returning toward the radar DUT 202 adds to zero.

[0087] Active cancellation comes from an auxiliary re-illuminator EC 730 that includes an auxiliary re-illuminator antenna 732. The re-illuminator creates a black dashed center region 734 (labeled "EC") at the center of the DOE 704. The auxiliary re-illuminator antenna 732 is located at some convenient transmission sidelobes of the DOE 704, where "transmission" refers to the Tx power from the radar DUT 202 that is neither absorbed nor reflected by the DOE 204. Calibration is performed where no target is simulated, but the auxiliary re-illuminator phase and gain are adjusted to minimize reception by the DUT. Specifically, the computer 112 controls the cancellation signals, but they are emitted from another re-illuminator antenna, such as the auxiliary re-illuminator antenna 732. The cancellation signals are incident at the center of the DOE 704 and refocused onto the radar DUT 702. This is very similar to noise-canceling headphones. A very convenient way to achieve this is to connect the MRD to the auxiliary re-illumination antenna 732 and choose its δf* so that the canceller distance matches the distance between the radar DUT 202 and the DOE 204, and the auxiliary δf* phase and VGA gain produce destructive interference with the specular reflection.

[0088] In view of the foregoing, the present disclosure, through one or more of its various aspects, embodiments, and / or specific features or subcomponents, is therefore intended to provide one or more of the advantages specifically noted below. For purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of the embodiments according to the present teachings. However, other embodiments consistent with the present disclosure that depart from the specific details disclosed herein are still within the scope of the appended claims. In addition, descriptions of well-known devices and methods may be omitted so as not to obscure the description of the example embodiments. Such methods and devices are within the scope of the present disclosure.

[0089] Although various target simulations for automotive radar systems have been described with reference to several representative embodiments, it should be understood that the words used are words of description and illustration, rather than words of limitation. Changes may be made within the scope of the appended claims, as presently described and amended, without departing from the scope and spirit of the dynamic return signal simulation for automotive radar sensor configurations in their aspects. Although the dynamic return signal simulation for automotive radar sensor configurations has been described with reference to specific apparatus, materials, and embodiments, the dynamic return signal simulation for automotive radar sensor configurations is not intended to be limited to the details disclosed; rather, the dynamic return signal simulation for automotive radar sensor configurations extends to all functionally equivalent structures, methods, and uses within the scope of the appended claims.

[0090] The description of the embodiments described herein is intended to provide a general understanding of the structure of each embodiment. Description is not intended to be used as a complete description of all elements and features of the disclosure described herein. After reading this disclosure, many other embodiments may be apparent to those skilled in the art. Other embodiments may be utilized and derived from this disclosure so that structural and logical replacements and changes may be made without departing from the scope of this disclosure. In addition, the diagram is merely representative and may not be drawn to scale. Some ratios in the diagram may be exaggerated, while other ratios may be minimized. Accordingly, this disclosure and the accompanying drawings are considered to be illustrative and non-restrictive.

[0091] One or more embodiments of the present disclosure may be referred to herein individually and / or collectively by the term "teaching", which is merely for convenience and is not intended to voluntarily limit the scope of the application to any specific invention or inventive concept. In addition, although specific embodiments have been shown and described herein, it should be understood that any subsequent arrangement designed to achieve the same or similar purpose can replace the specific embodiments shown. This disclosure is intended to cover any and all subsequent modifications or variations of various embodiments. The combination of the above embodiments and other embodiments not specifically described herein will be apparent to those skilled in the art upon review of the description.

[0092] An abstract of the disclosure is provided to comply with 37 CFR §1.72(B) and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Additionally, in the foregoing detailed description, various features may be grouped together or described in a single embodiment for the purpose of linking the disclosure as a whole. This disclosure should not be interpreted to reflect that the claimed embodiments require the use of more features than are expressly recited in each claim. Rather, as reflected in the appended claims, the subject matter of the present invention may be directed to fewer than all features of any one of the disclosed embodiments. Accordingly, the appended claims are incorporated into the detailed description, with each claim independently defining separately claimed subject matter.

[0093] The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to practice the concepts described in this disclosure. As such, the above-disclosed subject matter is to be considered illustrative rather than restrictive, and the appended claims are intended to cover all such modifications, improvements, and other embodiments that fall within the true spirit and scope of the disclosure. Therefore, to the maximum extent permitted by law, the scope of the disclosure is to be determined by the broadest permissible interpretation of the appended claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

1. A system (100) for testing a vehicle radar, comprising: a diffractive optical element (104) (DOE (104)) configured to diffract electromagnetic waves incident on the first side (103) from a radar device under test (DUT); and A re-illumination element adapted to receive electromagnetic waves diffracted from the diffractive optical element (104) from a second side (105), the re-illumination element adapted to emit electromagnetic waves with an apparent angle of arrival (AoA) back to the diffractive optical element (104), wherein the re-illumination element further comprises: a plurality of modulated reflective devices (MRDs (110)), each modulated reflective device comprising an antenna (108), a circulator (402), an in-phase quadrature (IQ) mixer (403), and a variable gain amplifier (VGA (404)).

2. The system (100) of claim 1, wherein the re-illumination element is adapted to simulate (10) an apparent target (2) distance, or an apparent target (2) velocity, or both.

3. The system (100) of claim 1, wherein the gain or loss of the variable gain amplifier (404) is selected to map a radar cross section to a corresponding one of a plurality of targets.

4. The system (100) of claim 1, wherein the plurality of modulated reflective devices (110) is equal to a plurality of targets.

5. The system (100) of claim 1 , wherein each of the plurality of modulated reflective devices (110) is connected to a corresponding one of a plurality of patch antenna arrays connected adjacent to one another, and the plurality of modulated reflective devices (110) and the plurality of patch antennas comprise a single re-illumination element.

6. The system (100) of claim 5, wherein the single re-illumination element is not gimbaled in the azimuthal direction.

7. The system (100) according to claim 5, wherein each of the plurality of patch antenna arrays comprises a plurality of patch antennas connected in series through a signal transmission line.

8. The system (100) of claim 7, wherein a phase of an electromagnetic wave traveling along a corresponding one of the plurality of patch antennas connected in series is substantially continuous.

9. The system (100) of claim 7, wherein the phase of electromagnetic waves traveling along adjacent arrays of the plurality of patch antennas has a varying electrical phase to scan in an azimuth direction.

10. The system (100) of claim 1, wherein each antenna (108) is a point-focused antenna (108).

11. The system (100) of claim 1, wherein the diffractive optical element (104) facilitates reducing electromagnetic waves specularly reflected from a first side (103) thereof.

12. A system (100) for testing a vehicle radar, comprising: a diffractive optical element (104) (DOE (104)) configured to diffract electromagnetic waves incident on the first side (103) from a radar device under test (DUT); a re-illumination element adapted to receive electromagnetic waves diffracted from the diffractive optical element (104) from a second side (105), the re-illumination element adapted to transmit electromagnetic waves with an apparent angle of arrival (AoA) back to the diffractive optical element (104), wherein the re-illumination element is adapted to simulate (10) an apparent target (2) distance, or an apparent target (2) velocity, or both, wherein the re-illumination element further comprises: a plurality of modulated reflective devices (MRDs (110)), each modulated reflective device comprising an antenna (108), a circulator (402), an in-phase quadrature (IQ) mixer (403), and a variable gain amplifier (VGA (404)); an active echo cancellation device connected to one of the plurality of modulated reflective devices (110), the active echo cancellation device having a frequency shift (δf*) and a gain of a variable gain amplifier (VGA (404)) selected to destructively interfere with electromagnetic radiation specularly reflected from the first side (103) of the diffractive optical element (104); and A controller (114) includes a memory (116) storing instructions and a processor (118) executing the instructions, wherein the controller (114) controls the re-illumination element and is configured to perform a performance test on the vehicle radar including a plurality of targets.

13. The system (100) of claim 12, wherein a number of the plurality of focal points is greater than or equal to a number of the plurality of targets being simulated by the system (100).

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