System and method for emulating echo signals from an emulated target with reduced interference from reflections

Abstract

The system and method emulates an echo signal from an emulated target in response to a radar signal from a radar DUT. The system includes an antenna configured to receive a radar signal and direct a reflected portion of the radar signal at a predetermined deflection angle away from the direction of incidence of the radar signal to prevent the radar DUT from receiving the reflected portion, and a transceiver configured to provide an RF signal having an RF frequency shifted from the frequency of the radar signal by an amount indicative of a distance to an emulated target, and to transmit the RF signal to the radar DUT as an emulated echo signal, The antenna pattern includes a peak beam angled away from normal incidence on the antenna at a beam squint angle that compensates for the predetermined deflection angle to direct the peak beam at the radar DUT.

Description

[Background technology]

[0001] Advanced driver-assistance systems (ADAS) and autonomous driving systems for vehicles rely on detection and ranging systems that use detecting and ranging electromagnetic signals, including, for example, millimeter-wave radar signals. Radar signals are used to warn of forward and rear collisions, to implement, for example, adaptive cruise control and autonomous parking, and ultimately, to perform autonomous driving on streets and highways. ADAS are promising because of their low cost and ability to operate at night or in severe weather conditions (e.g., fog, rain, snow, dust).

[0002] Conventional automotive radar systems typically have multiple transmitters and receivers on an ego vehicle. Actual driving environments in which radar systems may be deployed can vary widely, and many such driving environments can be complex. For example, real driving environments may contain numerous objects with complex reflection, diffraction, and multi-reflection characteristics that affect the echo signals responsive to the radar signal. Incorrect detection and / or interpretation (i.e., detection and / or interpretation) of echo signals can directly result in the triggering of false alarms or inappropriate responses, or the failure to trigger warnings or responses that should be triggered, which can ultimately lead to a collision. Therefore, reliable testing of radar systems is important.

[0003] However, road testing of ADAS and autonomous driving systems can be problematic and costly. Few local governments allow road testing of automated systems. Therefore, road testing does not offer much variety in terms of driving scenarios. Furthermore, those local governments that do allow road testing typically require an emergency driver in the driver's seat in case the automated system makes a critical error, and another person in the passenger seat to help monitor the emergency driver's actions and record other observations. This adds additional costs to road testing. Therefore, automakers and radar module vendors are eager to emulate driving conditions electronically, simulating a wide variety of driving scenarios without local government permission and reducing costs for emergency drivers and passengers.

[0004] Conventional systems for emulating echo signals reflected from multiple emulated targets typically include simulators that attempt to emulate the physics of the problem. For example, a conventional simulator may receive a radar signal transmitted from a radar under test, delay the radar signal by an amount corresponding to the propagation delay due to the range to the emulated target, scale the amplitude of the radar signal to account for the range and the radar cross section (RCS) of the target, and then retransmit the scaled and delayed signal to the radar under test, thereby emulating the transmission of the radar signal from the radar under test to the target and the reflection of the corresponding echo signal.

[0005] However, in conventional simulators, in addition to the return signals (emulated echo signals) from the emulated radar targets, unwanted external signals, sometimes referred to as "ghost targets," are generated. For example, receive / transmit antennas physically located in front of the simulator's pixels are not perfect absorbers and therefore reflect a portion of the radar signal. The reflected portion exhibits non-zero RCS at the setup range and angles of arrival (AoA) of the antenna itself. For example, patch array antennas, in particular, require the use of a ground plane, which is a major source of undesirable RCS. Ghost targets can cause the radar under test to erroneously conclude that an emulated radar target is present at the setup range (which can be less than one meter from the radar under test) or can interfere with proper detection of the emulated radar target itself and / or control of the vehicle in response to the detected emulated radar target (i.e., such detection and / or control). Summary of the Invention

[0006] The illustrative 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, dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a simplified block diagram illustrating a system for emulating echo signals of a radar device under test (DUT) with reduced interference from reflections, according to a representative embodiment. [Figure 2]FIG. 1 is a simplified block diagram of a patch array antenna of a radar target simulator (RTS) (e.g., a first RTS 121) in a system that emulates echo signals of a radar DUT, according to a representative embodiment. [Figure 3A] FIG. 1 is a simplified schematic diagram of an example of an unbalanced patch array antenna of an RTS for horizontal beam squint, according to a representative embodiment. [Figure 3B] FIG. 3B is a simplified block diagram of a portion of the unbalanced patch array antenna of FIG. 3A showing an implementation of a matching circuit for horizontal beam squinting, according to a representative embodiment. [Figure 4A] FIG. 1 is a simplified schematic diagram of an example of a balanced patch array antenna of an RTS for horizontal beam squint, according to a representative embodiment. [Figure 4B] FIG. 4B is a simplified block diagram of a portion of the balanced patch array antenna of FIG. 4A showing an implementation of a matching circuit for horizontal beam squint, according to a representative embodiment. [Figure 5A] FIG. 1 is a simplified schematic diagram of an example of an unbalanced patch array antenna of an RTS for vertical beam squint, according to a representative embodiment. [Figure 5B] FIG. 5B is a simplified block diagram of a portion of the unbalanced patch array antenna of FIG. 5A showing an implementation of a matching circuit for vertical beam squint, according to a representative embodiment. [Figure 6A] FIG. 1 is a simplified schematic diagram of an example of a balanced patch array antenna of an RTS for vertical beam squint, according to a representative embodiment. [Figure 6B] FIG. 6B is a simplified block diagram of a portion of the balanced patch array antenna of FIG. 6A showing an implementation of a matching circuit for vertical beam squint, according to a representative embodiment. [Figure 7]FIG. 1 is a simplified block diagram illustrating a system for emulating an echo signal with reduced interference, according to a representative embodiment. [Figure 8] FIG. 8 is a simplified block diagram of the exemplary RTS of FIG. 7 for emulating an echo signal with reduced interference from reflections, according to a representative embodiment. [Figure 9A] FIG. 2 is a simplified plan view of an example cavity-backed antenna of an RTS for horizontal or vertical beam squint, according to a representative embodiment. [Figure 9B] 9B is a simplified cross-sectional view of the cavity-back antenna of FIG. 9A according to a representative embodiment. [Figure 10] FIG. 1 is a flow diagram illustrating a method for emulating an echo signal with reduced interference from reflections, according to a representative embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following detailed description, for purposes of explanation and not limitation, exemplary embodiments disclosing specific details are described to provide a thorough understanding of an embodiment according to the present teachings. Descriptions of known systems, devices, materials, methods of operation, and methods of manufacture may be omitted to avoid obscuring the description of the exemplary embodiments. Nevertheless, systems, devices, materials, and methods within the understanding of those skilled in the art are within the scope of the present teachings and may be used in accordance with the exemplary embodiments. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. Defined terms have meanings commonly understood and accepted in the technical field of the present teachings, in addition to the scientific and technical meaning of the defined term.

[0009] Although terms such as first, second, and third may be used herein to describe various elements or components, it should be understood that these elements or components should not be limited by these terms. These terms are used only to distinguish one element or component from another. Thus, a first element or component discussed below could be referred to as a second element or component without departing from the teachings of the present disclosure.

[0010] The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. As used in this specification and the appended claims, the singular terms "a," "an," "the," or "the" are intended to include both the singular and the plural, unless the context clearly dictates otherwise. Furthermore, the term "comprises" and / or similar terms (i.e., the term "comprises" and / or similar terms) as used herein specify the presence of a referenced feature, element, and / or component (i.e., the feature, element, or component, or all of them), but do not preclude the presence or addition of one or more other features, elements, components, and / or groups thereof (i.e., other features, elements, components, or groups thereof, or all of them). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0011] Unless otherwise stated, when an element or component is said to be "connected," "coupled," or "adjacent" to another element or component, it is understood that the element or component can be directly connected or coupled to the other element or component, or there may be intervening elements or components. That is, these and similar terms include instances where one or more intervening elements or components may be used to connect the two elements or components. However, when an element or component is said to be "directly connected" to another element or component, this only includes instances where the two elements or components are connected to each other without any intervening or intervening elements or components.

[0012] The present disclosure is therefore intended to achieve one or more of the advantages, as specifically mentioned below, through one or more of its various aspects, embodiments, and / or specific features (i.e., aspects, embodiments, and / or specific features) or subcomponents. For purposes of explanation and not limitation, exemplary embodiments disclosing specific details are described to provide a thorough understanding of an embodiment in accordance with the present teachings. However, other embodiments that depart from the specific details disclosed herein but are not inconsistent with the present disclosure may still be within the scope of the appended claims. Furthermore, descriptions of known devices and methods may be omitted so as not to obscure the description of the exemplary embodiments. Such methods and devices are within the scope of the present disclosure.

[0013] Generally, a drive emulation system is provided that emulates echo signals from an emulated radar target in response to radar signal transmissions from a radar device under test (DUT) located on a vehicle under test, such as an automobile or other moving platform. Embodiments minimize interference from ghost targets, such as radar signals reflected from transmit and receive antennas and other system hardware, by directing reflected radar signals away from the radar DUT, thereby preventing the radar DUT from erroneously determining that the reflected radar signals represent the emulated radar target.

[0014] According to a representative embodiment, a system is provided for emulating an echo signal reflected from an emulated radar target in response to a radar signal transmitted by a radar DUT. The echo signal emulation system includes antennas configured to receive a radar signal over the air from the radar DUT. Each of the antennas is configured to reflect a portion of the radar signal and direct the reflected portion of the radar signal at a predetermined deflection angle away from the incident direction of the radar signal to prevent the radar DUT from receiving the reflected portion of the radar signal. The incident direction is substantially perpendicular to the wavefront of the radar signal transmitted by the radar DUT. For example, the antennas may be patch array antennas, each of which includes patch elements arranged in an array and a ground plane mirror, with the array, together with its ground plane, tilted at a blaze angle from the incident direction of the radar signal. Of course, other types of antennas may be incorporated without departing from the scope of the present teachings.

[0015] The echo signal emulation system further includes transceivers coupled to the antennas for receiving radar signals, each transceiver configured to mix the received radar signal with a locally generated signal having a frequency that provides as an output a radio frequency (RF) signal having an RF signal shifted from the radar frequency of the radar signal by an amount indicative of the distance to the emulated target, and transmit the RF signal via the antenna as an emulated echo signal to the radar DUT. Each antenna has an antenna pattern including a peak beam angled away from normal incidence at a beam squint angle, where the beam squint angle compensates for a predetermined deflection angle to direct the peak beam toward the radar DUT for receiving the radar signal and transmitting the RF signal. In this case, the beam squint angle has the same value as the blaze angle but points in the opposite direction, and the predetermined deflection angle is approximately twice the blaze angle.

[0016] According to another representative embodiment, a method for emulating an echo signal reflected from an emulated target in response to a radar signal transmitted by a radar DUT is provided, the method including: angling at least one antenna of an RTS at a blaze angle relative to a direction of incidence of the radar signal transmitted by the radar DUT; Near field outside the (e.g., mid-field or far fieldadjusting an antenna pattern of at least one antenna to angle a peak beam of the antenna pattern at a beam squint angle from normal incidence of the at least one antenna; receiving a radar signal over the air from a radar DUT using the adjusted antenna pattern and reflecting a portion of the radar signal away from the direction of incidence of the radar signal at a predetermined deflection angle due to a blaze angle of the at least one antenna to prevent the radar DUT from receiving the reflected portion of the radar signal; mixing the received radar signal with a locally generated signal having a frequency providing an RF signal having an RF frequency shifted from a radar frequency of the radar signal by an amount indicative of a distance to an emulated target; and transmitting the RF signal to the radar DUT as an emulated echo signal via the at least one antenna using the adjusted antenna pattern. The beam squint angle compensates for the predetermined deflection angle to direct the peak beam at the radar DUT for receiving the radar signal and transmitting the RF signal.

[0017] FIG. 1 is a simplified block diagram illustrating a system for emulating echo signals of a radar DUT with reduced interference (eg, ghost targets removed), according to a representative embodiment.

[0018] 1, system 100 includes multiple radar target simulators (RTSs) located within a test chamber, such as an anechoic chamber, at a setup range R from a radar under test or radar DUT 105. The setup range R is located within the radar DUT 105 for receiving radar signals and transmitting corresponding emulated echo signals. Near field Outside the near-field, e.g., mid-field or far fieldThe setup range R is in a far-field range. For example, the setup range R is at least about 0.75 meters from the radar DUT 105. The multiple RTSs include, for example, a first RTS 121, a second RTS 122, and an nth RTS 123, which are arranged in a planar array relative to one another. However, it is understood that the first RTS 121, the second RTS 122, and the nth RTS 123 may be arranged non-planarly without departing from the scope of the present teachings. For example, as described in U.S. Patent Application No. 17 / 157,160, filed January 25, 2021, by Gregory S. Lee et al., the entire contents of which are incorporated herein by reference, the first RTS 121, the second RTS 122, and the nth RTS 123 may form a curved array, such as a cylindrical or spherical array with the radar DUT 105 positioned at the center of curvature.

[0019] Each of the first RTS 121, the second RTS 122, and the nth RTS 123 includes hardware and software configured to receive radar signals from the radar DUT 105 and, in response to the received radar signals, generate emulated echo signals (return signals) reflected from emulated radar targets in a scene simulation. For example, each of the first RTS 121, the second RTS 122, and the nth RTS 123 may include one or more antennas, transceivers, and signal generators, as described below with reference to FIG. 3 , although any type of compatible RTS may be incorporated without departing from the scope of the present teachings. The one or more antennas may be, for example, patch array antennas, each of which includes patch elements arranged in a two-dimensional array. In an exemplary embodiment, each of the first RTS 121, the second RTS 122, and the nth RTS 123 may include a receive (Rx) patch array antenna for receiving radar signals from the radar DUT 105 and a transmit (Tx) patch array antenna for transmitting (retransmitting) emulated echo signals to the radar DUT 105. At least a portion of each of the first RTS 121, the second RTS 122, and the nth RTS 123 is assumed to present a substantially flat surface, as shown in FIG. 1. For example, each of the Rx patch array antenna and the Tx patch array antenna includes a ground plane mirror presenting a substantially flat surface.

[0020] The radar DUT 105 transmits a radar signal represented by a radar wavefront 130 in a direction of incidence 135 that is perpendicular to the radar wavefront 130. The first RTS 121, the second RTS 122, and the nth RTS 123 are arranged in a blazed array, meaning that they are tilted (slanted) at a slight blaze angle θ so that their corresponding substantially flat faces are angled away from the direction of incidence 135 of the radar signal. Because the first RTS 121, the second RTS 122, and the nth RTS 123 do not absorb all of the radar signal from the radar DUT 105, a portion of the radar signal, for example at the carrier frequency, will be reflected (scattered) from the first RTS 121, the second RTS 122, and the nth RTS 123 at normal incidence 145 from the second and nth RTSs 121, 122, and 123 perpendicular to the reflected wavefront 140. The reflected portion of the radar signal is directed away from the radar signal's direction of incidence 135 at a predetermined deflection angle φ, which in the illustrated configuration is equal to twice the blaze angle θ (2θ). The blaze angle θ is large enough so that the reflected portion of the radar signal is not received or otherwise detected by the radar DUT 105, thereby preventing the appearance of a ghost target based on the reflected portion. For example, the setup range R may be set up to place the first RTS 121, the second RTS 122, and the nth RTS 123 in the mid-field or far field Because the antennas are positioned at 100°, the blaze angle θ can be relatively small, for example, in the range of about 5 degrees to about 25 degrees. The value of the blaze angle θ also depends on the angular distance to which the peak beam of each antenna pattern can be squint, as explained below.

[0021] If the first RTS 121, the second RTS 122, and the nth RTS 123 each include one or more patch array antennas, the reflected portion of the radar signal will reflect from the ground plane as described above, but will also reflect from all surfaces parallel to the ground plane, such as the patch elements, the top surface of the dielectric on which the patch elements are disposed, an incomplete RTS radome, etc.

[0022] A disadvantage of tilting the first RTS 121, the second RTS 122, and the nth RTS 123 is that the respective antenna patterns of the corresponding antennas are similarly tilted, so that the radar DUT 105 may no longer be positioned within the peak beam of these antenna patterns. That is, referring to the first RTS 121 for illustration, if the antenna(s) have peak directivity at normal incidence 145, tilting the first RTS 121 results in a loss of gain with respect to receiving radar signals from the radar DUT 105 and / or transmitting emulated echo signals to the radar DUT 105 (i.e., receiving radar signals from the radar DUT 105, transmitting emulated echo signals to the radar DUT 105, or both). For example, if the gain reduction in one direction is approximately 2 dB, the net emulation loss is approximately 4 dB because signal strength is reduced in both the receive and transmit directions.

[0023] To compensate for this undesirable result, the antenna pattern of each of the first RTS 121, the second RTS 122, and the nth RTS 123 is modified using beam squinting. Beam squinting is the intentional peaking of the directivity of the antenna pattern at an angle away from the normal incidence of the antenna. In the illustrated embodiment, the beam squinting angle θ is set so that the peak beam 125 of the antenna pattern is away from the normal incidence 145 of the antenna in the first RTS 121. s The beam is squinted on the first RTS 121 so that it is angled at a blaze angle θ b is compensated for, and finally, a predetermined deflection angle φ of the reflected portion of the radar signal is compensated for. s directs the peak beam 125 to the radar DUT 105 to receive the radar signal and transmit the emulated echo signal. In one embodiment, the beam squint angle θ s is the blaze angle θ in the compensation direction bThe peak beam 125 represents both the receive and transmit antenna patterns, regardless of whether the first RTS 121 has a single antenna for both receive and transmit, or separate Rx and Tx antennas as described above. Thus, the first RTS 121 receives and transmits (retransmits) well in the direction of the radar DUT 105 while still preventing the appearance of ghost targets. In the illustrated configuration, the first RTS 121, the second RTS 122, and the nth RTS 123 are assumed to have the same antenna pattern and are tilted by the same amount. Therefore, the beam squints of the first RTS 121, the second RTS 122, and the nth RTS 123 will be the same.

[0024] If the antenna of the first RTS 121 is a patch array antenna, beam squint can be performed by adjusting the strategic phase relationship between adjacent rows of patch elements to increase radiation in a desired direction. The phase relationship can be controlled using a phase shifter, for example, to steer the peak beam 125, or the phase relationship can remain fixed. For purposes of explanation, the phase relationship of the patch array antenna is assumed to be fixed.

[0025] FIG. 2 is a simplified block diagram of a patch array antenna of an RTS (e.g., the first RTS 121) in a system that emulates the echo signals of a radar DUT, according to a representative embodiment.

[0026] 2, patch array antenna 221 is shown to include three representative patch elements, namely, first patch element 231, second patch element 232, third patch element 233, and nth patch element 234, in a single row of patches in the array for purposes of illustration. It should be understood that patch array antenna 221 may include fewer or more than three patch elements, which may be arranged in arrays of various sizes without departing from the scope of the present teachings. Also, for purposes of illustration, first patch element 231, second patch element 232, third patch element 233, and nth patch element 234 are in a horizontal arrangement and separated by a predetermined distance d.

[0027] The first patch element 231 has a phase φ, which is the input phase of the received or transmitted signal, and each successive adjacent patch element in the same row has a repeating phase change of Δφ. That is, the second patch element 232 has a phase φ+Δφ, the third patch element 233 has a phase φ+2Δφ, and the third patch element 234 has a phase φ+(n-1)Δφ. When the phase change of Δφ is zero (i.e., all patch elements have the same phase), the peak beam of the patch array antenna 221 is substantially perpendicular (broadside) to the ground plane mirror 210 of the patch array antenna 221, as indicated by arrow 240, and in that case, there is no peak beam squint. When the phase change of Δφ is non-zero, the peak beam of the patch array antenna 221 has a beam squint angle θ according to equation (1). s Only squints.

number

[0028] In equation (1), λ is the wavelength of the center frequency of the received radar signal or the transmitted emulated echo signal, and d is the distance between adjacent patch elements in the same row of the array. When the phase change Δφ is positive (as shown in the example of Figure 2), the beam squint angle θ sis also positive (to the right of the broadside arrow 240) as indicated by arrow 245. When the phase change Δφ is negative, the beam squint angle θ s is also negative (to the left of the broadside arrow 240).

[0029] In one embodiment, the patch elements are arranged on parallel microstrips extending from one or more feed lines, with the microstrips providing columns and adjacent patch elements on corresponding microstrips providing rows of the patch array antenna. Phase variations in the different microstrips can be implemented by matching networks with different line lengths feeding the different microstrips.

[0030] Figure 3A is a simplified schematic diagram of an example of an unbalanced patch array antenna of an RTS for horizontal beam squint, according to a representative embodiment. Figure 3B is a simplified block diagram of a portion of the unbalanced patch array antenna of Figure 3A showing an implementation of a matching circuit for horizontal beam squint, according to a representative embodiment.

[0031] Referring to FIG. 3A, the unbalanced patch array antenna 300 includes a feed line 310, a matching circuit 350, and patch elements P connected to the matching circuit 350 along four microstrips 341, 342, 343, and 344. 11 ~P 45 and patch element P 11 ~P 45are arranged in an array format with four parallel columns C1, C2, C3, and C4 (corresponding to microstrips 341-344) and five parallel rows R1, R2, R3, R4, and R5 for illustrative purposes. Of course, alternative array sizes can be incorporated without departing from the scope of the present teachings. Feed line 310 supplies an unbalanced signal to unbalanced patch array antenna 300. Feed line 310 connects to matching circuit 350, which includes matching feed lines that connect to microstrips 341-344, respectively. The matching feed lines have different lengths and provide different phases, as described below. Adjacent patch elements in the same row (e.g., patch element P in row R2) 32 and P 42 ) are equally separated by a distance d and adjacent patch elements in the same column (e.g., patch element P in column C4) 41 and P 42 ) are equally separated by a length l, which is the same as for an unbalanced patch array antenna configured to provide a broadside beam peak. Thus, the horizontal squint provided by the unbalanced patch array antenna 300 is a function of the different phases provided to the microstrips 341-344 by the matching circuit 350.

[0032] Referring to FIG. 3B, matching circuit 350 includes multiple phase shifters connected to microstrips 341-344 corresponding to columns C1, C2, C3, and C4, respectively. In the illustrated embodiment, unbalanced feedline 310 is divided into a first phase shifter 351 providing an arbitrary phase φ1 and a second phase shifter 352 providing an arbitrary phase φ1 with a phase change of 2Δφ (φ1+2Δφ). First phase shifter 351 is connected to a third phase shifter 353 providing a phase φ0 and a fourth phase shifter 354 providing an adjusted phase φ0+Δφ. Second phase shifter 352 is similarly connected to a fifth phase shifter 355 providing a phase φ0 and a sixth phase shifter 356 providing an adjusted phase φ0+Δφ. The phase and / or phase adjustment (i.e., phase and / or phase adjustment) provided by each of the first through sixth phase shifters 351 through 356 is, as described above, a function of the line lengths of the respective matching feed lines within matching circuit 350. These line lengths are indicated in FIG. 3A by the dashed ellipses labeled to correspond to the first through sixth phase shifters 351 through 356.

[0033] In the exemplary embodiment shown in FIGS. 3A and 3B, the peak beam of the unbalanced patch array antenna 300 is located at the patch element P 11 ~P 45 As columns C1-C4 of the unbalanced patch array antenna 300 have increasing total phase adjustment (increasing length of the matching lines) from left to right, they are squinted to the right by the squint angle (positive squint). Alternatively, the peak beam of the unbalanced patch array antenna 300 can be squinted to the left by the squint angle (negative squint) by increasing the total phase adjustment of columns C1-C4 from right to left. In general, for any squint direction, the larger the phase adjustment Δφ between adjacent columns C1-C4, the larger the resulting squint angle.

[0034] Figure 4A is a simplified schematic diagram of an example of a balanced patch array antenna of an RTS for horizontal beam squint, according to a representative embodiment. Figure 4B is a simplified block diagram of a portion of the balanced patch array antenna of Figure 4A showing an implementation of a matching circuit for horizontal beam squint, according to a representative embodiment.

[0035] Referring to FIG. 4A, the balanced patch array antenna 400 includes feed lines 411 and 412, a matching circuit 450, and patch elements P connected to the matching circuit 450 along four microstrips 341, 342, 343, and 344. 11 ~P 45 3A and 3B, the horizontal squint provided by the balanced patch array antenna 400 is a function of the different phases provided by the matching circuit 450 to the microstrips 341-344.

[0036] Referring to FIG. 4B, matching circuit 450 includes multiple phase shifters connected to microstrips 341-344 corresponding to columns C1, C2, C3, and C4, respectively. In the illustrated embodiment, balanced feedline 411 connects to a first phase shifter 451 providing an arbitrary phase φ1, and balanced feedline 412 connects to a second phase shifter 452 (φ1+2Δφ+180 degrees) providing an arbitrary phase φ1 with a phase shift of 2Δφ+180 degrees considering the differential signal. The first phase shifter 451 is connected to a third phase shifter 453 providing a phase φ0 and a fourth phase shifter 454 providing an adjusted phase φ0+Δφ. The second phase shifter 452 is similarly connected to a fifth phase shifter 455 providing a phase φ0 and a sixth phase shifter 456 providing an adjusted phase φ0+Δφ. The line lengths of each of the first through sixth phase shifters 451 through 456 are indicated in FIG. 4A by dashed ellipses labeled to correspond to the first through sixth phase shifters 451 through 456.

[0037] In the exemplary embodiment shown in FIGS. 4A and 4B, the peak beam of the balanced patch array antenna 400 is 11 ~P 45 Since columns C1-C4 of the balanced patch array antenna 400 have increasing phase adjustments from left to right, the peak beam of the balanced patch array antenna 400 is squinted to the right by the squint angle (positive squint). Alternatively, the peak beam of the balanced patch array antenna 400 can be squinted to the left by the squint angle (negative squint) by increasing the phase adjustments of columns C1-C4 from right to left.

[0038] Figure 5A is a simplified schematic diagram of an example of an unbalanced patch array antenna of an RTS for vertical beam squint, according to a representative embodiment. Figure 5B is a simplified block diagram of a portion of the unbalanced patch array antenna of Figure 5A showing an implementation of a matching circuit for vertical beam squint, according to a representative embodiment.

[0039] Referring to FIG. 5A, the unbalanced patch array antenna 500 includes a feed line 510, a matching circuit 550, and patch elements P connected to the matching circuit 550 along four microstrips 541, 542, 543, and 544. 11 ~P 44 and patch element P 11 ~P 44 are arranged in an array format with four parallel columns C1, C2, C3, and C4 (corresponding to microstrips 541-544) and five parallel rows R1, R2, R3, and R4 for purposes of illustration. Of course, alternative array sizes may be incorporated without departing from the scope of the present teachings. A feed line 510 supplies an unbalanced signal to the unbalanced patch array antenna 500. The feed line 510 is connected to a matching circuit 550 that includes matching feed lines connected to the microstrips 541-544, respectively. Adjacent patch elements in the same row (e.g., patch element P in row R3) are connected to a matching circuit 550 that includes matching feed lines connected to the microstrips 541-544, respectively. 32 and P 42 ) are equally separated by a distance d and adjacent patch elements in the same column (e.g., patch element P in column C4) 41 and P 42 ) are equally separated by length l. That is, rows R1, R2, R3, and R4 are arranged in parallel across microstrips 541-544, with adjacent rows offset from each other by an electrical angle distance (indicated by length l) to create a phase gradient between adjacent rows and provide a vertical beam squint angle for patch array antenna 500.

[0040] In particular, the length l separating adjacent patch elements in the same row determines the amount of upward or downward squint provided by the unbalanced patch array antenna 500. That is, when the length l is longer than the nominal length separating adjacent patch elements required to provide a broadside beam peak (as shown in FIG. 5A), the unbalanced patch array antenna 500 provides an upward (positive) beam squint. Conversely, when the length l is shorter than the nominal length, the unbalanced patch array antenna 500 provides a downward (negative) beam squint. Thus, the vertical squint provided by the unbalanced patch array antenna 500 is a function of the value of the length l separating the patch elements on each of the microstrips 541-544.

[0041] 5B, the matching circuit 550 includes a plurality of phase shifters connected to microstrips 541-544 corresponding to columns C1, C2, C3, and C4, respectively. 11 is a patch element P with a length of x+Δx. 12 separated from the patch element P 12 is also a patch element P with length x+Δx. 13 where x is, for example, the nominal full guide wavelength λ of, for example, a microstrip or coplanar waveguide (CPW). g The value of x is shorter than the free space wavelength λ because the dielectric constant of the substrate is greater than 1. In that case, Δx=λ g*Δφ / 2π, where Δφ is the same as described above with reference to equation (1) for horizontal beam squint. In the illustrated embodiment, the unbalanced feedline 510 is divided into a first phase shifter 551 and a second phase shifter 552, each of which provides an arbitrary phase φ. The first phase shifter 551 is connected to a third phase shifter 553 and a fourth phase shifter 554, each of which provides a phase φ. Similarly, the second phase shifter 521 is connected to a fifth phase shifter 555 and a sixth phase shifter 556, each of which also provides a phase φ. The phases of the various sets of phase shifters are made the same to provide phase matching. The phases are provided by the line lengths indicated in FIG. 5A by the dashed ellipses labeled to correspond to the first through sixth phase shifters 551 through 556. The vertical squint provided by the unbalanced patch array antenna 500 is a function of the length l, as described above.

[0042] As mentioned above, in the exemplary embodiment shown in FIGS. 5A and 5B, adjacent patch elements P on microstrips 541-544 11 ~P 44 Because the length l separating the lengths l is longer than the nominal length that would otherwise not provide squint, the peak beam of the unbalanced patch array antenna 500 is squinted upward by the squint angle. Alternatively, the length l can be reduced to be shorter than the nominal length that would not provide squint, causing the peak beam of the unbalanced patch array antenna 500 to squint downward by the squint angle. In general, for any squint direction, the greater the difference between the length l and the nominal length, the greater the resulting upward or downward squint angle.

[0043] Figure 6A is a simplified schematic diagram of an example of a balanced patch array antenna of an RTS for vertical beam squint, according to a representative embodiment. Figure 6B is a simplified block diagram of a portion of the balanced patch array antenna of Figure 6A showing an implementation of a matching circuit for vertical beam squint, according to a representative embodiment.

[0044] Referring to FIG. 6A, a balanced patch array antenna 600 includes feed lines 611 and 612, a matching circuit 650, and patch elements P connected to the matching circuit 650 along four microstrips 541, 542, 543, and 544. 11 ~P 44 The feedlines 611 and 612 provide a differential signal to the balanced patch array antenna 600. The feedlines 611 and 612 connect to a matching circuit 650 which includes matching feedlines that connect to the microstrips 541-544, respectively, to provide the desired phase. Again, the vertical squint provided by the balanced patch array antenna 600 is achieved by providing a phase shift between adjacent patch elements P on the microstrips 541-544. 11 ~P 44 The balanced patch array antenna 600 provides an upward (positive) beam squint when the length l is longer than the nominal length separating adjacent patch elements required to provide a broadside beam peak (as shown in FIG. 6A). Conversely, when the length l is shorter than the nominal length, the balanced patch array antenna 600 provides a downward (negative) beam squint.

[0045] Referring to FIG. 6B, matching circuit 650 includes multiple phase shifters connected to microstrips 541-544 corresponding to columns C1, C2, C3, and C4, respectively. In the illustrated embodiment, balanced feedline 611 is connected to a first phase shifter 651, which provides an arbitrary phase φ1. Balanced feedline 612 is connected to a second phase shifter 652, which provides an arbitrary phase φ1+180 degrees, taking into account the differential signal (φ1+180). First phase shifter 651 is connected to a third phase shifter 653 and a fourth phase shifter 654, each of which provides a phase φ0. Similarly, second phase shifter 621 is connected to a fifth phase shifter 655 and a sixth phase shifter 656, each of which also provides a phase φ0. The phase is provided by the line lengths shown in Figure 6A by the dashed ellipses labeled to correspond to the first through sixth phase shifters 651 through 656. In the exemplary embodiment shown in Figures 6A and 6B, adjacent patch elements P on microstrips 541 through 544 11 ~P 45 is longer than the nominal length that would otherwise not provide squint, so that the peak beam of the balanced patch array antenna 600 is squinted upward (positive beam squint). Alternatively, the peak beam of the balanced patch array antenna 600 can be squinted downward (negative beam squint) by reducing the length l to be shorter than the nominal length that would not provide squint.

[0046] As described above, the RTS and corresponding one or more antennas can be incorporated into a drive emulation system that emulates an echo signal from an emulated radar target in response to a radar signal transmission from the radar DUT. FIG. 7 is a simplified block diagram illustrating an exemplary system for emulating an echo signal from a radar DUT with reduced interference (e.g., ghost targets removed) according to a representative embodiment. As will be understood by those skilled in the art with the benefit of this disclosure, one likely vehicle radar is an automotive radar used in various capacities in current and emerging automotive applications. Another emulation example is an in-vehicle person detection system, where the radar is configured to detect the presence or absence of people / children / pets in potentially harmful situations, such as in a car parked with the windows open on a hot, sunny day. However, it is emphasized that the echo signal emulation system described herein is not limited to automotive radar systems and can be applied to other types of vehicles that can use vehicle radar systems, including, for example, trucks, buses, motorcycles, bicycles, mopeds (e.g., scooters), and aircraft.

[0047] 7, an echo signal emulation system 700 is arranged to test a radar DUT 105, which may be configured to transmit a frequency-modulated continuous wave (FMCW) radar signal and receive a return signal including an emulated echo signal that emulates reflections (echoes) of the radar signal from targets in a scene emulation. The echo signal emulation system 700 may also work with some phase-modulated continuous wave (PMCW) systems. The radar DUT 105 includes one or more radar transmitters and corresponding transmit antennas, and one or more radar receivers and corresponding receive antennas. All or a portion of the system 700 may be contained within a test chamber, such as an anechoic test chamber.

[0048] The system 700 includes multiple re-illuminators 706, each including at least one antenna 708 and at least one RTS 710. The RTS 710 can be, for example, a frequency-offset transceiver or mini-RTS (mRTS). The antenna 708 can be, for example, a patch antenna array or, as described above, a cavity-backed antenna. As described in more detail below, each RTS (frequency-offset transceiver) 710 generally includes receiver circuitry, transmitter circuitry, and an in-phase (I)-quadrature (Q) mixer (I / Q mixer). A signal generator 730 generates I and Q signals that are input to the I / Q mixer and mixed with the radar signal. The signal generator 730 can be, for example, a direct digital synthesizer (DDS), a field-programmable gate array (FPGA), and a digital-to-analog converter (DAC). The I / Q mixer can be considered part of both the receiver circuitry and the transmitter circuitry. The received radar signal may be input to the I / Q mixer as a local oscillator (LO) signal at the LO port, and the I and Q signals generated by the signal generator 730 may be input to the I / Q mixer as intermediate frequency (IF) signals at the IF port, for example. The mixed product of the LO and IF signals may be output by the I / Q mixer as an RF signal at the RF port, for example, where the RF signal has an RF frequency slightly shifted from the carrier frequency of the radar signal. The RF signal is amplified / attenuated as necessary and transmitted by the transmitter circuitry to the radar DUT 105 via the antenna 708 as an emulated echo signal. In the case of an FMCW radar signal, the frequency and magnitude of the emulated echo signal indicate the emulated range and RCS of the emulated target.For example, in the case of an FMCW radar signal using a chirp signal, the smaller the frequency difference between the RF frequency of the emulated echo signal within the linear ramp of the chirp signal and the emulated echo signal, the closer the emulated target will appear to the radar DUT 105. Generally, distance information is extracted from the frequency difference, and RCS information is provided by the magnitude of the emulated echo signal.

[0049] In an alternative configuration, the signal generator 730 may not be physically included in each of the re-illuminators 706 without departing from the scope of the present teachings, in which case one signal generator 730 may provide I and Q signals for multiple RTSs 710. In this configuration, the signal generator 730 may be implemented using a single source, such as an FPGA and DAC, capable of creating independent I and Q signal frequencies for each RTS 710.

[0050] There may be one reilluminator 706 for each emulated target in the scene emulation. Alternatively, one reilluminator 706 may be used for multiple emulated targets, including one or more scattering targets and / or one or more non-scattering targets (i.e., one or more scattering targets and / or one or more non-scattering targets). In one embodiment, the reilluminators 706 may be arranged in a 2D array, where each reilluminator 706 represents an element in the 2D array. In this case, the element having a spatial location corresponding to an emulated target will generate an emulated echo signal corresponding to that target.

[0051] The system 700 also includes a computer 740 having a controller 744. The controller 744 described herein may include a combination of a memory 746 that stores instructions and an exemplary processor 748 that executes the stored instructions to implement all or a portion of the processes described herein. A database 720 may store information used for target emulation, including various predetermined scenarios having one or more targets. For example, the database 720 may store desired characteristics of point targets, such as range, RCS, velocity, acceleration, etc., from the radar DUT 105. The database 720 may further store information regarding parameters of a particular radar DUT 105, such as code, power, field of view, etc. The radar DUT 105 may be connected to the computer 740 by various types of wired and / or wireless network connections (i.e., wired and / or wireless network connections). The controller 744 is configured to control the operation of the RTS 710 and the signal generator 730 via control signals indicated by dashed lines.

[0052] The controller 744 can be housed within or linked to a workstation, display / monitor, and one or more input devices (e.g., keyboard, joystick, and mouse) in the form of a standalone computing system, such as a computer or another assembly of one or more computing devices, a client computer, desktop, or tablet in a server system. The term "controller," as understood in the art of this disclosure and as illustratively described in this disclosure, broadly encompasses all structural configurations of application-specific mainboards or application-specific integrated circuits that control the application of various principles as described in this disclosure. The structural configuration of the controller 144 can include, but is not limited to, processor(s), computer-usable / computer-readable storage medium(s), operating system, application module(s), peripheral device controller(s), slot(s), and port(s), as discussed below.

[0053] Additionally, although computer 740 and / or controller 744 (i.e., computer 740, controller 744, or both) are shown as networked components, multiple components may be integrated into a single system. For example, computer 740 and / or controller 744 may be integrated with a display (not shown) and / or system 700 (i.e., display or system 700, or both). On the other hand, the networked components of computer 740 and / or controller 744 may be spatially dispersed, such as by being spread across different rooms or different buildings, in which case the networked components may be connected via a data connection. In yet another embodiment, one or more of the components of computer 740 and / or controller 744 are not connected to other components via a data connection, but instead are manually provided with input and / or output (i.e., input or output, or both), such as by a memory stick or other form of memory. In yet another embodiment, the functionality described herein, while based on the functionality of elements of computer 740 and / or controller 744, may be performed outside of system 700.

[0054] In the illustrated embodiment, computer 740 includes memory 746, a controller 744 including a processor 748, and a user and / or network interface (not shown) and a display (not shown) (i.e., a user and / or network interface and / or a display). Computer 740 and / or controller 744 may be implemented as a processing unit. In various embodiments, the processing unit may include one or more computer processors (e.g., processor 748), digital signal processors (DSPs), central processing units (CPUs), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), or combinations thereof, using any combination of hardware, software, firmware, hardwired logic, or combinations thereof. Each of the computer 740, the controller 744, and / or the processor 748 (i.e., the controller 744 and / or the processor 748) may include its own processing memory (e.g., memory 746) that stores computer-readable code (e.g., software, software modules) that enables the execution of various functions described herein. For example, the processing memory may store software instructions / computer-readable code executable by the processing unit (e.g., a computer processor) to perform some or all aspects of the methods described herein, including various steps of the methods described below with reference to FIG. 9. That is, execution of the instructions / computer-readable code generally causes the processing unit of the computer 740 and / or the controller 744 to emulate an echo signal reflected from an emulated radar target in response to a radar signal transmitted by the radar DUT 105.

[0055] Memory 746, and any other memory described herein (including database 720), can be various types of random access memory (RAM), read-only memory (ROM), and / or other storage media (i.e., various types of random access memory, read-only memory, and / or other storage media), including flash memory, electrically programmable read-only memory (EPROM), electrically erasable and programmable read-only memory (EEPROM), compact disk read-only memory (CD-ROM), digital versatile disk (DVD), registers, latches, flip-flops, hard disk, removable disk, tape, floppy disk, Blu-ray disk, or universal serial bus (USB) driver, or any other form of storage media known in the art, which are tangible and non-transitory (e.g., as compared to a transitory propagated signal). Memory can be volatile or non-volatile, secure and / or encrypted (i.e., secure and / or encrypted), or non-secure and / or unencrypted (i.e., unsecure and / or unencrypted) without departing from the scope of the present teachings. Memory 746 and database 720 can represent one or more memories and databases, as well as multiple memories and databases, including distributed and network-connected memories and databases.

[0056] Generally, in operation, the radar DUT 105 emits an RF radar signal (illustratively, a mm-wave signal) that is focused onto a respective one of the antennas 708 (beneficially, relatively high-gain antennas) of one of the re-illuminators 706. The antennas 708 may be patch array antennas or cavity-back antennas selected for the wavelength of the signals received from the radar DUT 105. Of course, other types of antennas may be incorporated as the antennas 708 without departing from the scope of the present teachings.

[0057] As described above, each of the antennas 708 is tilted (together with the corresponding redirector 706) to reflect a portion of the radar signal transmitted by the radar DUT 105, thereby directing the reflected portion of the radar signal at a predetermined deflection angle away from the incident direction of the radar signal to prevent the radar DUT 105 from receiving the reflected portion of the radar signal. The antenna patterns of the antennas 708 are modified to compensate for the tilt of the antennas 708, such that the peak beam of each antenna 708 is squint at an angle directed toward the radar DUT 105, increasing the gain of the antenna 708 in that direction.

[0058] The radar signal incident on the antenna 708 is provided to each of the RTSs 710. Based on input from the controller 744, a frequency shift of the incident radar signal is performed in each of the RTSs 710 to advantageously emulate the distance of the target from the radar DUT 105, the velocity of the target relative to the radar DUT 105, or both. In addition, the azimuth angle (the +x direction in the coordinate system of FIG. 7) and the elevation angle (the +z direction in the coordinate system of FIG. 7) are emulated by the antenna 708. The antenna 708 may be part of an electronically steerable antenna array of the reilluminator 706. Similarly, the reilluminator 706 may be mechanically moved instead of or in addition to the antenna 708. The emulated echo signal provided by the RTS 710 is incident on the radar DUT 105. The computer 740 receives signals from the radar DUT 105 for further analysis of the accuracy of the radar DUT 105.

[0059] Typically, radars utilizing FMCW waveforms operate by transmitting an RF radar signal, for example, in the 77 GHz band. The radar signal is modulated so that its instantaneous frequency varies linearly from a first frequency to a second frequency over a predetermined period of time, referred to as a chirp signal. The RF frequency can rise linearly over the predetermined period of time (an upchirp), where the first frequency (e.g., 77 GHz) is lower than the second frequency (e.g., 78 GHz), or the RF frequency can fall linearly over the predetermined period of time (a downchirp), where the first frequency (e.g., 78 GHz) is higher than the second frequency (e.g., 77 GHz). This linear ramp in frequency is repeated to form a continuous wave signal transmitted from the radar.

[0060] The transmitted radar signal propagates toward the target at the speed of light, reflects off the target, and returns to the radar as a reflected echo signal, delayed by the round-trip time between the radar and the target. The length of this delay corresponds to the distance between the radar and the target. The echo signal is then mixed with the radar signal currently being transmitted at the radar, an operation known as homodyne reception. The resulting IF signal has a frequency equal to the instantaneous difference between the frequency of the received echo signal and the frequency of the radar signal currently being transmitted at the radar.

[0061] That is, due to the delay in the received echo signal and the linear slope in frequency of the transmitted radar signal over a given period, there will be a frequency difference between the currently transmitted radar signal (which is changing linearly in frequency) and the received echo signal (which is at the frequency of the originally transmitted radar signal). This frequency difference is therefore proportional to the round-trip delay multiplied by the frequency sweep rate in Hertz per second (Hz / s). For example, because closer targets have less delay than more distant targets, closer emulated targets will result in a smaller frequency difference and therefore a lower IF signal frequency than more distant emulated targets. If the emulated target is a point target, the resulting IF signal will be a single tone at a single frequency. If the emulated target includes multiple targets, the resulting IF signal will have multiple tones with frequencies corresponding to the instantaneous range to each target. In the general case of considering N targets, the radar IF signal will include N tones, each frequency corresponding to the range to the corresponding target, and each amplitude corresponding to the relative received strength of the echo signal from that target. In particular, the received power is a function of the range from the radar to the target and the target's reflectivity per the target's RCS. For a given target RCS, the power is generally a function of 1 / R 4 where R is the distance between the radar and the target.

[0062] In this context, exemplary embodiments of the present disclosure utilize a frequency offset provided by the RTS 710 to emulate the range from the radar DUT 105 to the emulated target. Using the frequency offset, each emulated target is indicated by an effective frequency shift due to propagation delay. However, rather than delaying the transmission of the echo signal to indicate range, the delay itself is emulated by a frequency offset transceiver that provides an expected frequency shift corresponding to the desired delay for the echo signal. For example, as discussed in more detail below, the radar signal transmitted from the radar DUT 105 can be mixed in the RTS 710 with a frequency offset signal using a single-sideband (SSB) mixer. The frequency offset signal has a frequency (or pattern of frequencies) equal to the desired frequency shift that would be present in the echo signal corresponding to the delay (or round-trip difference). In practice, the frequency offset signal is precisely the form of the desired IF signal at the radar DUT 105 when it receives the echo signal and mixes it with the currently transmitted radar signal. Therefore, a single emulated target at a first range will result in an IF signal at the radar DUT 105 consisting of a single tone having a frequency representing the range to the single target. This can be generated using an SSB mixer in the RTS 710 by using the desired IF signal as a frequency offset signal. Multiple emulated targets will result in an IF signal consisting of multiple tones. Therefore, using this multi-tone IF signal as an offset signal will result in echo signals that emulate multiple emulated targets.

[0063] 8 is a simplified block diagram of the exemplary re-illuminator (and corresponding RTS and frequency offset transceiver) of FIG. 7 emulating an echo signal with reduced interference from reflections, according to an exemplary embodiment. Aspects of the RTS described with respect to this exemplary embodiment may be common to all RTSs.

[0064] Referring to FIG. 8 , the reilluminator 706 includes an antenna 708 and an RTS 710 connected to the antenna 708, as described above. Of course, in practice, there may be more than one RTS 710 in the system, and therefore more than one antenna 708 (e.g., as shown in the exemplary embodiment of FIG. 7 ). The antenna 708 is configured to receive a radar signal 801 over the air from the radar DUT 105. The RTS 710 is configured to generate an emulated echo signal 820 in response to the radar signal indicative of an emulated target, where the emulated echo signal 820 is transmitted by the antenna 708 and received by the radar DUT 105. The emulated echo signal 820 indicates the range of the emulated target from the radar DUT 105, for example, based on a scene emulation stored in the database 720. In addition, a reflected portion 822 of the radar signal is reflected by the antenna 708 and the RTS 710. If uncorrected, the reflected portion 822 may be received by the radar DUT 105, creating ghost targets and interfering with the emulated echo signal 820.

[0065] In the illustrated embodiment, the RTS 710 includes a circulator 802, an I / Q mixer 803, and a signal generator 730. The circulator 802 enables the RTS 110 to use a single antenna 708 to receive a radar signal 801 from the radar DUT 105 and transmit an emulated echo signal 820 to the radar DUT 105. Alternatively, the antenna 708 can be implemented as separate receive and transmit antennas without departing from the scope of the present teachings, in which case the circulator 802 can be omitted.

[0066] The I / Q mixer 803 can be, for example, an SSB mixer with a standard 90-degree phase shift for radar signals, resulting in an output of either the upper sideband (USB) with the lower sideband (LSB) removed, or the LSB with the USB removed. The signal generator 730 can be implemented, for example, using a direct digital synthesizer (DDS), or an FPGA and a digital-to-analog converter (DAC), although other types of controllable signal generators can be incorporated without departing from the scope of the present teachings. The signal generator 730 can be controlled, for example, by a computer 740, to provide I and Q signals of various amplitudes and phases. The signal generator 730 can also be controlled to separately adjust the DC values (DC offsets) of the I and Q signals, as discussed below.

[0067] In the illustrated embodiment, the I / Q mixer 803 comprises an LO port, an RF port, and an IF port, where the LO port is configured to receive the radar signal 801 from the antenna 708 as an LO signal, and the IF port is configured to receive the I signal and the Q signal from the signal generator 730. The I / Q mixer 803 mixes the radar signal with the I signal and the Q signal and outputs the mixing product as an RF signal from the RF port, for example, after amplification and / or attenuation (i.e., amplification and / or attenuation), to ultimately provide the emulated echo signal 820. Although not shown, it is understood that the RTS 710 may further comprise signal processing components, such as filters, attenuators, and / or amplifiers (i.e., amplifiers and / or attenuators), to process the radar signal 801 before it is input to the I / Q mixer as the LO signal.

[0068] The RF signal output from the I / Q mixer 203 may be provided to a gain controller 804, such as a variable gain amplifier (VGA) or output attenuator, with a gain control input 805. As mentioned above, the gain control input 805 of the gain controller 804 may be controlled by the computer 740. The gain controller 804 further enables appropriate emulation of an echo signal 820 in response to a radar signal 801 from the radar DUT 105 at the antenna 708. In particular, the power of the emulated echo signal 820 from the antenna 708 is indicative of the RCS of the emulated target. Thus, the gain or attenuation provided by the gain controller 804 is selected at the gain control input 805 based on the power of the radar signal incident on the antenna 708 and the RCS of the emulated target at the desired emulation distance.

[0069] The RF signal is transmitted by the RTS 710 back to the radar DUT 105 via the antenna 708. As described above, the antenna pattern 824 of the antenna 708 is adjusted so that the peak beam 825 of the antenna pattern 824 is squint at an angle that directs the peak beam 825 in a direction toward the radar DUT 105. This beam squint compensates for the blaze angle of the antenna 708, so that the maximum gain of the antenna pattern is directed toward the radar DUT 105 for receiving the radar signal 801 and transmitting the emulated echo signal 820, but the antenna 708 is angled away from the incident direction of the radar signal 801 to deflect the reflected portion 822 away from the radar DUT 105.

[0070] Further description of echo signal emulation systems is provided, for example, in U.S. Patent Application No. 17 / 148230 to Christian Bourde et al., filed January 13, 2021, the entire contents of which are incorporated herein by reference.

[0071] Generally, control of the retransmitted power is used to emulate a consistent RCS, which can be stored, for example, in a lookup in a table in database 720. To that end, for a given range R to an emulated target, the amplitude (strength) of the returned echo signal is proportional to the RCS, as 1 / R 4 It is known that the noise level decreases as √√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√√ 4Emphasis is placed on providing a return echo signal strength to the radar DUT 105 that conforms to radar decay laws and corresponds to the RCS tolerance. According to exemplary embodiments, signal strength (and therefore power) is adjusted by adjusting the strength of the I and Q signals, with weaker I and Q signals providing a relatively weaker emulated echo signal. Notably, in certain exemplary embodiments, the computer 740 pre-calculates a consistent return echo signal to be provided to a single focal point at the radar DUT 105, and the controller 744 then adjusts the strength of the I and Q signals to achieve this SSB strength. Alternatively, and advantageously, the gain or attenuation of the gain controller of the RTS 710 can be adjusted to control the SSB strength of the return echo signal.

[0072] If the radar DUT 105 is an FMCW device, the range / velocity is emulated electronically using the RTS 710. To do so, FMCW radar systems use chirp waveforms, as described above, whereby correlation of the original transmit (Tx) waveform from the radar DUT 105 with the received (Rx) echo waveform reveals the target range. For example, ±k sw In an up-chirp / down-chirp system with a chirp rate (measured in Hz / s), a target at a distance d and at zero relative velocity with respect to the host vehicle carrying the radar DUT 105 will experience a frequency shift (δf) given by equation (2), 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 105. δf=±(2k sw d / c) Equation (2)

[0073] The sign of the shift depends on which part of the waveform (up-chirp vs. down-chirp) is being processed. In contrast, Doppler shift due to relative velocity manifests itself as a "common-mode" frequency shift; for example, a pure upshift across both halves of the waveform indicates that the radar DUT is approaching a target. Correlation is performed in the radar DUT's IF / baseband processor, where a bandwidth of several MHz is typical.

[0074] Commonly deployed variations of FMCW radar systems use repeated up-chirps or repeated down-chirps, but not both (with dead time in between). Thus, the range to the emulated target is determined as in the previous paragraph, but now without the sign issue. Relative velocity is determined by measuring the phase shift between successive frame IF correlation signals, where frame is a term used in the art to refer to one period of the waveform. In many FMCW radar applications, the frame repetition rate is typically a few kHz to tens of kHz.

[0075] Of course, types of antennas with steerable peak beams other than patch array antennas may be incorporated for use with the RTS without departing from the scope of the present teachings. For example, in an alternative embodiment, the antenna(s) of each RTS may be a cavity-backed antenna that includes a plated air cavity in a substrate and a dipole antenna disposed on the substrate above the air cavity so that the air cavity acts as a reflector. Figure 9A is a simplified plan view of an example cavity-backed antenna of an RTS for vertical beam squint, according to a representative embodiment, and Figure 9B is a simplified cross-sectional view of the cavity-backed antenna of Figure 9A along line A-A', according to a representative embodiment.

[0076] 9A and 9B, plated cavity-back antenna 900 includes feedlines 911 and 912 connected to dipole antenna 920, which includes four representative antenna elements 921, 922, 923, and 924 formed on antenna dielectric 940 (transparent in FIG. 9A ) above a reflective air cavity 950. Of course, alternative types of antennas and / or antenna elements (i.e., antenna and / or antenna elements) configurable to radiate downward into air cavity 950 may be incorporated without departing from the scope of the present teachings. Plated cavity-back antenna 900 further includes printed circuit board (PCB) 930, with air cavity 950 formed to a depth D within PCB 930. The PCB 930 may be formed from three layers, including, for example, a bottom copper layer, a dielectric layer, and a top copper layer, and the air cavity 950 may be formed through the top copper and dielectric layers. The air cavity 950 is plated with a conductive plating, which may be formed of copper, for example, to provide a cavity floor 951 and cavity sidewalls 955, which allow the air cavity 950 to act as a reflector for the dipole antenna 920. In the illustrated configuration, the dipole antenna 920 radiates into the air cavity 950 through the antenna dielectric 940, is reflected at the cavity floor 951 and sidewalls 955, and re-radiates upward through the antenna dielectric 940.

[0077] The antenna pattern of the plated cavity-back antenna 900, including the direction of the peak beam, is a function of the position of the dipole antenna 920 relative to the air cavity 950. The shape and depth of the air cavity 950 generally affect the overall performance of the plated cavity-back antenna 900. Therefore, by changing the relative position of the dipole antenna 920, the antenna pattern of the dipole antenna 920 can be changed to provide a desired beam squint angle. The shape and depth of the air cavity 950 generally affect the overall performance of the plated cavity-back antenna 900.

[0078] For example, if a plated cavity-back antenna is designed to radiate without a squint angle, the dipole antenna's phase center is positioned over the cavity's physical center. If the dipole antenna's phase center is positioned elsewhere within the cavity, the resulting antenna pattern will have a peak beam that is squinted in a direction and amount determined by the relationship between the phase center and the cavity's physical center. For example, in FIG. 9A , antenna phase center 926 (the center of antenna elements 921, 922, 923, and 924) is positioned toward the cavity front (CF) relative to cavity physical center 956. Thus, dipole antenna 920 is reflected at a squint angle opposite the direction in which antenna phase center 926 is offset from cavity physical center 956—in the illustrated example, toward the cavity back (CB). Generally, the more the antenna phase center 926 is offset from cavity physical center 956, the greater the amount of beam squint.

[0079] Similarly, dipole antenna 920 can be reflected at a squint angle toward the cavity front, CF, by offsetting antenna phase center 926 from cavity physical center 956 toward the cavity back, CB. Also, dipole antenna 920 can be reflected at a squint angle toward the right and left of the air cavity by offsetting antenna phase center 926 from cavity physical center 956 toward the left and right, respectively. Thus, in general, the direction of the beam squint can be effectively steered in a different direction, approximately 180 degrees opposite, from the offset direction in which antenna phase center 926 is positioned from cavity physical center 956. The direction and amount of beam squint can be determined empirically.

[0080] 10 is a flow diagram illustrating a method for emulating an echo signal in response to a radar signal transmitted by a radar DUT with reduced interference from reflections, according to a representative embodiment. The method can be implemented, for example, by the above-described system 100 and / or system 700 (i.e., system 100, system 700, or both) under the control of computer 740.

[0081] Referring to FIG. 1 , in block S1011, at least one antenna of an RTS (e.g., RTSs 121, 122, 123) is angled away from the incident direction of a radar signal transmitted by the radar DUT. This angle may be referred to as a blaze angle. The blaze angle determines how much of the reflected portion of the radar signal emitted from the radar DUT in the incident direction is reflected back into the mid-field or far field (i.e., Near field The RTS has a reflecting surface that is sufficiently large so that a reflected portion from at least one antenna and other surfaces of the RTS located outside the RTS is reflected in a direction that bypasses the radar DUT.

[0082] In block S1012, the antenna pattern of the at least one antenna is adjusted (squinted) to angle the peak beam of the antenna pattern away from normal incidence of the at least one antenna toward the radar DUT at a beam squint angle. The beam squint angle thus ensures that the at least one antenna is angled away from the direction of incidence of the radar signal such that the maximum gain of the antenna pattern is still directed toward the radar DUT.

[0083] In block S1013, a radar signal is received over the air from the radar DUT at at least one antenna using the adjusted antenna pattern. A reflected portion of the radar signal is reflected by the at least one antenna and other surfaces of the RTS away from the direction of incidence of the radar signal at a predetermined deflection angle determined by a blaze angle of the at least one antenna. The predetermined deflection angle is twice the blaze angle.

[0084] In block S1014, the received radar signal is mixed with the generated IF signal by a frequency offset transceiver, as described above, to provide an RF signal having an RF frequency shifted from the radar frequency of the radar signal by an amount indicative of the range to the emulated target. The RF signal is amplified / attenuated as necessary to accurately represent the RCS of the emulated target.

[0085] In block S1015, the RF signal is transmitted to the radar DUT as an emulated echo signal via at least one antenna using the adjusted antenna pattern. The beam squint angle of the adjusted antenna pattern compensates for a predetermined deflection angle to direct a peak beam toward the radar DUT to receive the radar signal and transmit the RF signal. The radar under test receives the emulated echo signal without interference caused by reflected portions of the radar signal, thereby avoiding the appearance of ghost targets.

[0086] While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustrations and descriptions are to be considered illustrative or exemplary and not restrictive, and the invention is not limited to the disclosed embodiments. Those skilled in the art will understand and can make other variations to the disclosed embodiments when practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere recitation of certain measures in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0087] Aspects of the present invention may be embodied as an apparatus, a method, or a computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be collectively referred to herein as a "circuit," "module," or "system." Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer-readable medium(s) having computer-executable code embodied therein.

[0088] While exemplary embodiments are disclosed herein, those skilled in the art will recognize that many variations are possible in accordance with the present teachings and are within the scope of the appended claims. Accordingly, the invention is not to be limited except as by the scope of the appended claims. The claims as originally filed are as follows: Claim 1: 1. A system for emulating an echo signal reflected from an emulated target in response to a radar signal transmitted by a radar device under test (radar DUT), comprising: at least one antenna positioned outside a near field of the radar DUT and configured to receive the radar signal over the air from the radar DUT, the at least one antenna configured to reflect a portion of the radar signal and direct the reflected portion of the radar signal at a deflection angle away from a direction of incidence of the radar signal to prevent the radar DUT from receiving the reflected portion of the radar signal, wherein the direction of incidence is substantially perpendicular to a wavefront of the radar signal; a transceiver coupled to the at least one antenna for receiving the radar signal, the transceiver configured to mix the received radar signal with a generated signal having a frequency to provide a radio frequency (RF) signal having an RF shifted from a radar frequency of the radar signal by an amount indicative of a distance to the emulated target, and transmit the RF signal as an emulated echo signal via the at least one antenna to the radar DUT; Equipped with the at least one antenna has an antenna pattern including a peak beam angled at a beam squint angle away from normal incidence on the at least one antenna, the beam squint angle compensating for the predetermined deflection angle to direct the peak beam at the radar DUT to receive the radar signal and transmit the IF signal. Claim 2: 2. The method of claim 1, wherein the at least one antenna includes a patch array antenna, the patch array antenna comprising a ground plane mirror tilted at a blaze angle from the direction of incidence of the radar signal, and the predetermined deflection angle is approximately twice the blaze angle. system. Claim 3: The system of claim 2 , wherein the blaze angle is the same value as the squint angle and is opposite to the squint angle. Claim 4: The patch array antenna comprises: a plurality of microstrips extending in parallel from at least one feed source; a plurality of patch elements connected to the plurality of microstrips and arranged in parallel rows across the plurality of microstrips, adjacent rows of the plurality of rows being offset from one another by an electrical angle distance to create a phase gradient between the adjacent rows and provide the beam squint angle of the patch array antenna; The system of claim 2 further comprising: Claim 5: The system of claim 4 , wherein the at least one power source comprises an unbalanced port. Claim 6: The system of claim 4 , wherein the at least one power supply source comprises a balanced differential port. Claim 7: 10. The system of claim 1, wherein the at least one antenna includes a plated cavity-back antenna comprising a plated air cavity in a substrate and a dipole antenna disposed on the substrate above the air cavity such that the air cavity acts as a reflector, wherein a position of the dipole antenna relative to a cavity physical center of the air cavity changes the antenna pattern of the dipole antenna to provide the beam squint angle of the cavity-back antenna. Claim 8: 8. The system of claim 7, wherein the beam squint angle is in an opposite direction from an offset position of an antenna phase center of the dipole antenna from the cavity physical center. Claim 9: The system of claim 1 , wherein the predetermined deflection angle and the squint angle lie in a plane substantially perpendicular to the direction of incidence of the radar signal. Claim 10: 2. The system of claim 1, wherein the predetermined deflection angle and the squint angle lie in a plane that is substantially horizontal to the direction of incidence of the radar signal. Claim 11: 1. A method for emulating an echo signal reflected from an emulated target in response to a radar signal transmitted by a radar device under test (radar DUT), comprising: Angling at least one antenna of a radar target simulator (RTS) at a blaze angle relative to a direction of incidence of a radar signal transmitted by the radar DUT, the at least one antenna being outside a near field of the radar DUT; adjusting an antenna pattern of the at least one antenna to angle a peak beam of the antenna pattern away from normal incidence on the at least one antenna at a beam squint angle; receiving a radar signal over the air from the radar DUT using the adjusted antenna pattern and reflecting a portion of the radar signal away from the direction of incidence of the radar signal at a predetermined deflection angle due to the blaze angle of the at least one antenna to prevent the radar DUT from receiving the reflected portion of the radar signal; mixing the received radar signal with a locally generated signal having a frequency to provide a radio frequency (RF) signal having an RF shifted from a radar frequency of the radar signal by an amount indicative of a distance to the emulated target; transmitting the RF signal as an emulated echo signal via the at least one antenna to the radar DUT using the adjusted antenna pattern; Including, The beam squint angle compensates for the predetermined deflection angle to direct the peak beam toward the radar DUT for receiving the radar signal and transmitting the RF signal. Claim 12: 12. The method of claim 11, wherein the at least one antenna includes a patch array antenna, the patch array antenna having a ground plane mirror tilted at the blaze angle from the direction of incidence of the radar signal, and the predetermined deflection angle is approximately twice the blaze angle. Claim 13: The method of claim 12 , wherein the blaze angle has the same value as the squint angle and is opposite to the squint angle. Claim 14: 12. The method of claim 11 , wherein the at least one antenna comprises a plated cavity-back antenna having an air cavity plated in a substrate, and a dipole antenna disposed on the substrate above the air cavity such that the air cavity acts as a reflector, wherein a position of the dipole antenna relative to a cavity physical center of the air cavity changes the antenna pattern of the dipole antenna to provide the beam squint angle of the cavity-back antenna. Claim 15: 15. The method of claim 14, wherein the beam squint angle is in an opposite direction from an offset position of an antenna phase center of the dipole antenna from the cavity physical center. Claim 16: The method of claim 11 , wherein the predetermined deflection angle and the squint angle lie in a plane substantially perpendicular to the direction of incidence of the radar signal. Claim 17: The method of claim 11 , wherein the predetermined deflection angle and the squint angle lie in a plane that is substantially horizontal to the direction of incidence of the radar signal. Claim 18: 1. An antenna system for receiving radar signals transmitted by a radar device under test (radar DUT) outside a near field of the radar DUT, and for transmitting emulated echo signals reflected from an emulated target to the radar DUT in response to the radar signals, the antenna system comprising: a plurality of microstrips extending in parallel from at least one feed source; a plurality of matching feedlines connected to the plurality of microstrips; a plurality of patch elements connected to the plurality of microstrips and arranged in parallel rows across the plurality of microstrips; a ground plane for the plurality of patch elements, at least the ground plane being angled to reflect a portion of the radar signal away from a direction of incidence of the radar signal at a predetermined deflection angle to prevent the radar DUT from receiving the reflected portion of the radar signal, wherein the direction of incidence is substantially perpendicular to a wavefront of the radar signal; and Equipped with an antenna system, wherein an antenna pattern of the antenna system includes a peak beam angled at a beam squint angle away from normal incidence on the ground plane, the beam squint angle compensating for the predetermined deflection angle to direct the peak beam toward the radar DUT to receive the radar signal and transmit the emulated echo signal. Claim 19: 20. The antenna system of claim 18, wherein the squint angle is substantially in a horizontal plane relative to the direction of incidence of the radar signal and is a function of a length of each of the plurality of matching feedlines. Claim 20: 20. The antenna system of claim 18, wherein the squint angle is in a plane substantially perpendicular to the direction of incidence of the radar signal and is a function of a length between adjacent patch elements on each of the plurality of microstrips.

Claims

1. 1. A system for emulating an echo signal reflected from an emulated target in response to a radar signal transmitted by a radar device under test (radar DUT), comprising: at least one antenna positioned outside a near field of the radar DUT and configured to receive the radar signal over the air from the radar DUT, the at least one antenna configured to reflect a portion of the radar signal and transmit the reflected portion of the radar signal angled at a predetermined deflection angle away from a direction of incidence of the radar signal, the direction of incidence of the radar signal being substantially perpendicular to a wavefront of the radar signal, to reduce reception of the reflected portion of the radar signal by the radar DUT; a transceiver coupled to the at least one antenna for receiving the radar signal, the transceiver configured to mix the received radar signal with a generated signal having a frequency to provide an RF signal having a radio frequency (RF) shifted from the radar frequency of the radar signal by an amount indicative of a distance to the emulated target, and transmit the RF signal as an emulated echo signal via the at least one antenna to the radar DUT; Equipped with 1. A system for receiving the radar signal and transmitting the IF signal, wherein the at least one antenna has an antenna pattern including a peak beam angled at a beam squint angle away from a direction of incidence normal to a surface of the at least one antenna, the beam squint angle being angled to compensate for the predetermined deflection angle to direct the peak beam toward the radar DUT.

2. 2. The system of claim 1, wherein the at least one antenna includes a patch array antenna, the patch array antenna comprising a ground plane mirror tilted at a blaze angle from the direction of incidence of the radar signal, the predetermined deflection angle being approximately twice the blaze angle.

3. The system of claim 2 , wherein the blaze angle is the same value as the squint angle and is opposite to the squint angle.

4. The patch array antenna comprises: a plurality of microstrips extending in parallel from at least one feed source; a plurality of patch elements connected to the plurality of microstrips and arranged in parallel rows across the plurality of microstrips, adjacent rows of the plurality of rows being offset from one another by an electrical angle distance to create a phase gradient between the adjacent rows and provide the beam squint angle of the patch array antenna; The system of claim 2 further comprising:

5. The system of claim 4 , wherein the at least one power source comprises an unbalanced port.

6. The system of claim 4 , wherein the at least one power supply source comprises a balanced differential port.

7. 10. The system of claim 1, wherein the at least one antenna comprises a plated cavity-back antenna comprising a plated air cavity in a substrate and a dipole antenna disposed on the substrate above the air cavity such that the air cavity acts as a reflector, wherein a position of the dipole antenna relative to a cavity physical center of the air cavity changes the antenna pattern of the dipole antenna to provide the beam squint angle of the cavity-back antenna.

8. 8. The system of claim 7, wherein the beam squint angle is in an opposite direction from an offset location of an antenna phase center of the dipole antenna from the cavity physical center.

9. The system of claim 1 , wherein the predetermined deflection angle and the squint angle lie in a plane substantially perpendicular to the direction of incidence of the radar signal.

10. The system of claim 1 , wherein the predetermined deflection angle and the squint angle lie in a plane that is substantially horizontal to the direction of incidence of the radar signal.

11. 1. A method for emulating an echo signal reflected from an emulated target in response to a radar signal transmitted by a radar device under test (radar DUT), comprising: Angling at least one antenna of a radar target simulator (RTS) at a blaze angle relative to a direction of incidence of a radar signal transmitted by the radar DUT, the at least one antenna being outside a near field of the radar DUT; adjusting an antenna pattern of the at least one antenna to angle a peak beam of the antenna pattern away from a direction of incidence normal to a surface of the at least one antenna at a beam squint angle; receiving a radar signal over the air from the radar DUT using the adjusted antenna pattern and transmitting a reflection of a portion of the radar signal away from the direction of incidence of the radar signal at a predetermined deflection angle due to the blaze angle of the at least one antenna to reduce reception of the reflected portion of the radar signal by the radar DUT; mixing the received radar signal with a locally generated signal having a frequency to provide a radio frequency (RF) signal having an RF shifted from the radar frequency of the radar signal by an amount indicative of a distance to the emulated target; transmitting the RF signal as an emulated echo signal via the at least one antenna to the radar DUT using the adjusted antenna pattern; Including, The beam squint angle compensates for the predetermined deflection angle to direct the peak beam toward the radar DUT for receiving the radar signal and transmitting the RF signal.

12. 12. The method of claim 11 , wherein the at least one antenna includes a patch array antenna, the patch array antenna having a ground plane mirror tilted at the blaze angle from the direction of incidence of the radar signal, and the predetermined deflection angle is approximately twice the blaze angle.

13. The method of claim 12 , wherein the blaze angle has the same value as the squint angle and is opposite to the squint angle.

14. 12. The method of claim 11 , wherein the at least one antenna comprises a plated cavity-back antenna having an air cavity plated in a substrate, and a dipole antenna disposed on the substrate above the air cavity such that the air cavity acts as a reflector, and wherein a position of the dipole antenna relative to a cavity physical center of the air cavity changes the antenna pattern of the dipole antenna to provide the beam squint angle of the cavity-back antenna.

15. 15. The method of claim 14, wherein the beam squint angle is in an opposite direction from an offset position of an antenna phase center of the dipole antenna from the cavity physical center.

16. The method of claim 11 , wherein the predetermined deflection angle and the squint angle lie in a plane substantially perpendicular to the direction of incidence of the radar signal.

17. The method of claim 11 , wherein the predetermined deflection angle and the squint angle lie in a plane that is substantially horizontal to the direction of incidence of the radar signal.

18. 1. An antenna system for receiving radar signals transmitted by a radar device under test (radar DUT) outside a near field of the radar DUT, and for transmitting emulated echo signals reflected from an emulated target to the radar DUT in response to the radar signals, the antenna system comprising: a plurality of microstrips extending in parallel from at least one feed source; a plurality of matching feedlines connected to the plurality of microstrips; a plurality of patch elements connected to the plurality of microstrips and arranged in parallel rows across the plurality of microstrips; a ground plane for the plurality of patch elements, at least the ground plane being angled to transmit reflections of a portion of the radar signal away from a direction of incidence of the radar signal at a predetermined deflection angle to reduce reception of the reflected portion of the radar signal by the radar DUT, wherein the direction of incidence is substantially perpendicular to a wavefront of the radar signal; and Equipped with an antenna pattern of the antenna system including a peak beam angled at a beam squint angle away from a normal incidence direction on a surface of the ground plane, the beam squint angle compensating for the predetermined deflection angle to direct the peak beam toward the radar DUT to receive the radar signal and transmit the emulated echo signal.

19. 20. The antenna system of claim 18, wherein the squint angle is substantially in a horizontal plane relative to the direction of incidence of the radar signal and is a function of a length of each of the plurality of matching feedlines.

20. 20. The antenna system of claim 18, wherein the squint angle is in a plane substantially perpendicular to the direction of incidence of the radar signal and is a function of a length between adjacent patch elements on each of the plurality of microstrips.

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