System and method for clutter cancellation in radar systems

Abstract

A system, clutter cancellation circuit and a method generate a clutter cancellation signal for radar by receiving, at the clutter cancellation circuit, a radar transmission signal generated by a radar transmitter, and generating, by the clutter cancellation circuit, the clutter cancellation signal by attenuating, delaying and phase shifting the received radar transmission signal using attenuator, a signal delay, and a phase shifter in any order. The clutter cancellation signal can then be used to cancel one or more clutter signals within a radar return signal.

Description

SYSTEM AND METHOD FOR CLUTTER CANCELLATION IN RADAR SYSTEMSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 562,995 filed on March 8, 2024 and entitled “Clutter Cancellation and Other Related Methods”.TECHNICAL FIELD OF THE INVENTION

[0002] The present invention relates in general to the field of radar systems, and more particularly, to a system and method for clutter cancellation in radar systems.STATEMENT OF FEDERALLY FUNDED RESEARCH

[0003] This invention was made with government support under Grant / Contract Nos. ECCS- 2030094 and ECCS-1808613 awarded by the National Science Foundation (NSF). The government has certain rights in the invention.BACKGROUND OF THE INVENTION

[0004] Without limiting the scope of the invention, its background is described in connection with passive radar systems.

[0005] Frequency-modulated continuous-wave (FMCW) radars have quickly become an attractive solution for numerous ranging and sensing systems. New developments in automotive radar [1], [2], industrial sensing [3], [4], physical activity monitoring [5], [6], and home health tracking [7], [8] that leverage FMCW radar are rapidly emerging. FMCW range detection is accomplished by transmitting an electromagnetic wave, whose frequency is modulated periodically [9],

[0010] . This variable frequency wave propagates through the environment and is scattered by targets and clutter in the sensing environment. This scattered signal is then down converted by the radar receiver. For FMCW radar using a ramp waveform, the time delay caused by propagation and electronic delay produces a beat frequency in the baseband spectrum proportional to the range of the target. However, stationary clutter at a range similar to that of the target produces a similar beat frequency, making it difficult to resolve the target from clutter

[0011] , The fast Fourier transform (FFT) may be used in both the fast-time and slow-time dimensions in order to extract both the range and Doppler information of moving targets, allowing them to beresolved even if they would normally be concealed by stationary clutter. This technique, however, requires that the target maintains motion

[0012] , which is not practical for many applications. Computationally intense techniques may be used to suppress clutter

[0013] ; however, a strong clutter signal can still impact detection ability if the receiver is overdriven. Previous works have shown that RF feedforward is capable of suppressing self-interference but have not shown the ability to cancel the effects of stationary clutter located away from the sensor

[0014] , Beam steering may be used to provide angular resolution

[0015] ,

[0016] ,

[0017] but requires many antennas and increases the system’s size and power use.

[0006] Accordingly, there is a need for a system and method for clutter cancellation in radar systems.SUMMARY OF THE INVENTION

[0007] Various embodiments of the present disclosure provide a clutter cancellation technique that utilizes adaptive RF feedforward to achieve dynamic clutter compensation and improve the detection abilities of FMCW radar in practical applications. Clutter cancellation is achieved by controlling the amplitude and time delay of a feedforward signal to negate the effects of stationary clutter in the RF domain without either increasing the data processing load or restricting the radar’s operating point.

[0008] One embodiment of the present disclosure provides a method for generating a clutter cancellation signal. A radar transmission signal is generated by a radar transmitter and received by a clutter cancellation circuit. The clutter cancellation circuit generates a clutter cancellation signal by attenuating, delaying and phase shifting the received radar transmission signal using an attenuator, a signal delay, and a phase shifter in any order.

[0009] In one aspect, the method further includes combining the clutter cancellation signal with a radar return signal from one or more radar receiver antennas, wherein the radar return signal contains one or more target signals and one or more clutter signals. In another aspect, the clutter cancellation signal substantially cancels out the one or more clutter signals. In another aspect, the method further includes manually or automatically adjusting or tuning one or more of the attenuator, the signal delay and the phase shifter using a controller. In another aspect, theP fix attenuator attenuates the received radar transmission signal by an attenuation factor a — — - ,thePrx2Rr signal delay delays the received radar transmission signal by a time delay IdAC= — , where PRXcis a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light. In another aspect, a power of the signals received from a target and the clutter is Y GT Y G D Y 2,PRX— — — - — ’ where PTXis a transmit power, GTXis a transmit antenna gam, GRXis a receive antenna gain, o is a radar cross section (RCS), is a free space wavelength, and R is a distance. In another aspect, the cancellation signal operates in the radio frequency domain. In another aspect, the attenuator operates within a 2-18 GHz range and the phase shifter operates within a de- 18 GHz range. In another aspect, the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters. In another aspect, the cancellation signal improves the resolution and detection accuracy of a radar. In another aspect, the cancellation signal is effective when a target is stationary or moving.

[0010] Another embodiment of the present disclosure provides a clutter cancellation circuit for a radar that includes an attenuator, a signal delay and a phase shifter communicably coupled to one another in any order and configured to receive a radar transmission signal generated by a transmitter of the radar. The attenuator is configured to attenuate the received radar transmission signal. The signal delay is configured to delay the received radar transmission signal. The phase shifter is configured to phase shift the received radar transmission signal. The attenuator, the signal delay and the phase shifter are configured to generate a clutter cancellation signal.

[0011] In one aspect, the clutter cancellation signal is combined with a radar return signal from one or more radar receiver antennas, and the radar return signal contains one or more target signals and one or more clutter signals. In another aspect, the clutter cancellation signal substantially cancels out the one or more clutter signals. In another aspect, one or more of the attenuator, the signal delay and the phase shifter are manually or automatically adjusted or tuned using a controller. In another aspect, the attenuator attenuates the received radar transmission signal by an attenuation factor a = -^£- the signal delay delays the received radar transmission signal byPTX2Rr a time delay IdAC— where PRXcis a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light. In another aspect, a power of the signals received from a target and the clutter is PRX= -, where PTXis a transmit power, GTXis a transmit antenna gain, GRXis a receive antenna gain, o is a radar cross section (RCS), is a free space wavelength, and R is a distance. In another aspect, the cancellation signal operates inthe radio frequency domain. In another aspect, the attenuator operates within a 2-18 GHz range, and the phase shifter operates within a de- 18 GHz range. In another aspect, the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters. In another aspect, the cancellation signal improves the resolution and detection accuracy of a radar. In another aspect, the cancellation signal is effective when a target is stationary or moving.

[0012] Another embodiment of the present disclosure provides a system including a radar having a transmitter communicably coupled to one or more transmitter antennas and a receiver communicably coupled to one or more receiver antennas. One or more clutter cancellation circuits are communicably coupled between a transmission path from the transmitter to the one or more transmitter antennas and a reception path from the one or more receiver antennas to the receiver. Each clutter cancellation circuit includes an attenuator, a signal delay and a phase shifter communicably coupled to one another in any order and configured to receive a radar transmission signal from the transmission path. The attenuator is configured to attenuate the received radar transmission signal. The signal delay is configured to delay the received radar transmission signal. The phase shifter is configured to phase shift the received radar transmission signal. The attenuator, signal delay and phase shifter are configured to generate a clutter cancellation signal. The clutter cancellation signal is combined with a radar return signal in the reception path, which contains one or more target signals and one or more clutter signals from the one or more receiver antennas.

[0013] In one aspect, the clutter cancellation signal substantially cancels out the one or more clutter signals. In another aspect, one or more of the attenuator, the signal delay and the phase shifter are manually or automatically adjusted or tuned using a controller. In another aspect, the attenuator attenuates the received radar transmission signal by an attenuation factor a —the2Rr signal delay delays the received radar transmission signal by a time delay ldAC— where PRX(:is a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light. In another aspect, a power of the signals received from a target and the clutter is PRXwhere PTXis a transmit power, Grxis a transmit antenna gain, GRXis areceive antenna gain, o is a radar cross section (RCS), A. is a free space wavelength, and R is a distance. In another aspect, the cancellation signal operates in the radio frequency domain. Inanother aspect, the attenuator operates within a 2-18 GHz range, and the phase shifter operates within a de- 18 GHz range. In another aspect, the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters. In another aspect, the cancellation signal improves the resolution and detection accuracy of a radar. In another aspect, the cancellation signal is effective when a target is stationary or moving.

[0014] Note that the invention is not limited to the embodiments described herein, instead it has the applicability beyond the embodiments described herein. The brief and detailed descriptions of this disclosure are given in the following.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

[0016] FIG. 1 depicts an example of a FMCW active clutter cancellation system negating the impacts of clutter on FMCW ranging through adaptive cancellation at the transceiver in accordance with one embodiment of the present disclosure.

[0017] FIG. 2(a) is a graph illustrating that a strong static clutter creates an area of low resolution in the range spectrum in an FMCW radar system without clutter cancellation.

[0018] FIG. 2(b) is a graph illustrating the spectrum produced by an FMCW radar system with clutter cancellation in accordance with one embodiment of the present disclosure.

[0019] FIG. 3 depicts a simulation flowchart used to evaluate the impact of adaptive cancellation on FMCW radar detection in accordance with one embodiment of the present disclosure.

[0020] FIG. 4 depicts a block diagram of a clutter canceller in accordance with one embodiment of the present disclosure.

[0021] FIG. 5 depicts an experimental setup to measure the impact of feedforward cancellation on detection ability near clutter in accordance with one embodiment of the present disclosure.

[0022] FIG. 6 depicts a range spectrum evaluating the performance of adaptive cancellation in accordance with one embodiment of the present disclosure.

[0023] FIG. 7 depicts a method for generating a clutter cancellation signal in accordance with one embodiment of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0024] While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

[0025] To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not limit the invention, except as outlined in the claims.

[0026] Various methods are described below to provide an example of each claimed embodiment. They do not limit any claimed embodiment. Any claimed embodiment may cover methods that are different from those described above and below. The drawings and descriptions are for illustrative, rather than restrictive, purposes.

[0027] This disclosure presents a clutter cancellation technique that utilizes adaptive RF feedforward to achieve dynamic clutter compensation and improve the detection abilities of FMCW radar in practical applications. Clutter cancellation is achieved by controlling the amplitude and time delay of a feedforward signal to negate the effects of stationary clutter in the RF domain without either increasing the data processing load or restricting the radar’s operating point. The adaptive cancellation solution is presented and then examined through a time-domain FMCW radar simulation. The adaptive cancellation solution is verified experimentally using a passive canceller to provide the time and amplitude shift to negate the effects of stationary clutter.

[0028] Now referring to FIG. 1, an example of a FMCW active clutter cancellation system 100 negating the impacts of clutter on FMCW ranging through adaptive cancellation at the transceiver in accordance with one embodiment of the present disclosure is shown. The system 100 includes a FMCW radar 102 having a transmitter antenna 104, a receiver antenna 106 and a clutter canceller (also referred to as a clutter cancellation circuit) 108 communicably coupled betweenthe transmitter antenna 104 and the receiver antenna 106. The clutter canceller 108 will be described in more detail below. In this example, the target 110 is sitting in a chair 112 next to a standing lamp 1 14. The radar 100 transmits a signal 1 16 via the transmitter antenna 104 and receives a return signal via the receiver antenna 106 that includes both a target signal 118 and a clutter signal 120.

[0029] Note that the radar 100 can be any suitable radar having any number of antennas 104, 106 and any number of clutter cancellation circuits 108. Some non-limiting examples of radars may include; (1) PCT Patent Application No. PCT / US25 / 12032 filed on January 17, 2025 and entitled “Fast Startup Baseband Amplifier”, which claims priority to U.S. Provisional Patent Application No. 63 / 622,700 filed on January 19, 2022 and entitled “Fast Startup Baseband Amplifier”; and (2) PCT Patent Application No. PCT / US23 / 06650 filed on January 13, 2023 and entitled “Microwave Architecture for Passive Sensing Applications”, which claims priority to U.S. Provisional Patent Application No. 63 / 299,942 filed on January 15, 2022 and entitled “Microwave Architecture for Passive Sensing Applications”. The foregoing patent applications are hereby incorporated by reference in their entirety

[0030] As will be described below in more detail, each clutter cancellation circuit 108 includes an attenuator, a signal delay and a phase shifter communicably coupled to one another in any order. Each clutter cancellation circuit is communicably coupled between a transmission path from the transmitter to the one or more transmitter antennas and a reception path from the one or more receiver antennas to the receiver. A radar transmission signal in the transmission path is divided into two or more paths, one of which is used to create the clutter cancellation signal. The attenuator is configured to attenuate the received radar transmission signal. The signal delay is configured to delay the received radar transmission signal. The phase shifter is configured to phase shift the received radar transmission signal. The attenuator, signal delay and phase shifter are configured to generate a clutter cancellation signal. The clutter cancellation signal is combined with a radar return signal in the reception path containing one or more target signals and one or more clutter signals from the one or more receiver antennas.

[0031] In one aspect, the clutter cancellation signal substantially cancels out the one or more clutter signals. In another aspect, one or more of the attenuator, the signal delay and the phase shifter are manually or automatically adjusted or tuned using a controller. In another aspect and as described below, the attenuator attenuates the received radar transmission signal by anP f^X f attenuation factor a — — the signal delay delays the received radar transmission signal by a Prx2,R time delay ldAC= — , where PRXcisapower received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light. In another aspect, a power of the signals received from a target and the clutter is PRXwhere PTXis a transmit power, GTXis atransmit antenna gain, GRXis a receive antenna gain, o is a radar cross section (RCS), is a free space wavelength, and R is a distance. In another aspect, the cancellation signal operates in the radio frequency domain. In another aspect, the attenuator operates within a 2-18 GHz range, and the phase shifter operates within a de- 18 GHz range. In another aspect, the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters. In another aspect, the cancellation signal improves the resolution and detection accuracy of a radar. In another aspect, the cancellation signal is effective when a target is stationary or moving.

[0032] In FMCW ranging radar, the finite bandwidth of the sensor imposes limitations on the range resolution of the sensor that can obscure targets in the presence of strong static clutter

[0018] , In an FMCW radar system without clutter cancellation, a strong static clutter creates an area of low resolution in the range spectrum illustrated by FIG. 2(a) by total signal 202 (solid black line), where the target signal 118 (green dotted line) cannot be effectively resolved because of the clutter signal 120 (red dashed line). The distances to the target 110 and clutter (chair 112 and standing lamp 114) are denoted by the vertical gray lines. Even with sufficient range resolution, a strong clutter signal can impact the detection ability of the radar by reducing the maximum gain before saturating the receiver and preventing weak target signals from being detected. If, however, a system 100 including a clutter canceller illustrated in FIG. 1 is employed, clutter cancellation may be performed at the RF front end by combining the received signal with a delayed and attenuated copy of the transmitted signal to destructively interfere with only the clutter’s backscatter, producing the spectrum 210 (black solid line) shown in FIG. 2(b) and isolating the signal produced by the target. In this system, detection can be performed in the presence of clutter while maintaining simple signal processing requirements and boosting the effective range resolution of the sensor. It is worth noting that although full cancellation may require a polarity change, effective cancellation can be performed if the bandwidth is sufficiently low relative to the chirp period, as will be evident through simulation and experimental results with realistic bandwidth values.

[0033] In order to evaluate the impact of the theoretical cancellation technique, a simulation is developed to allow for rapid parameter adjustments. The overall simulation block diagram is illustrated in FIG. 3. Based on the desired target and clutter ranges and radar cross section (RCS) values, the FSPL, target, and clutter models solve for the relative power of the signals received from the target and clutter using the formulawhere PTXis the transmit power, GTXand GRXare the transmit and receive antenna gains, respectively, o is the RCS, is the free space wavelength, and J? is the distance. Given the clutter’s location, the adaptive cancellation model finds the required time delay and linear attenuation to cancel the clutter usingwhere PRXcand Rcare the power received from the clutter and the clutter distance, respectively, and c is the speed of light. Radar parameters, such as bandwidth, transmit power, and receiver gain, are then used to synthesize the resulting time-domain local oscillator (LO) signal and to calculate the received time domain RF signals from the target, clutter, and canceller usingfor each received signal, where B is the radar bandwidth. The RF signal is then down converted to create a baseband time domain signal. Digital filtering followed by windowing and FFT creates the final range spectrum for evaluation. The simulation is first tested assuming a radar with a 5- dBm transmit power, antenna gains of 6 dBi, and a 400-MHz bandwidth and corresponding 0.375- m range resolution without feedforward cancellation. The response is simulated with a target at 5.3 m from the radar and two clutters with a 1-m2RCS at 5 and 7 m. The resulting range spectrum is shown in FIG. 2(a) along with the spectra for both the target-only and clutter-only cases. It is seen from the results that the target cannot be resolved when its absolute distance to the radar is near that of the clutter due to limited range resolution. By precisely controlling the delay and attenuation of the feedforward path, however, the clutters’ response can be removed to improve the range resolution. A second simulation including a cancellation signal is implemented to verifythis theory, producing the range spectrum shown in FIG. 2(b). These results illustrate that the target distance can be clearly extracted after removing the impact of multiple clutters without requiring an increase in computational load or sensor complexity.

[0034] The phase shifter’s output versus the input is given below, where y(t) is the output, x(t) is the input, and AT is the programmed time -delay. y(t) = x(t - T) (5)For pure sinusoids, this translates to a phase shift that is dependent on the center frequency. For signals with a bandwidth, however, it is more convenient and intuitive to simply consider the phase shifter as a method of finely adjusting the time delay of the feedforward clutter cancellation signal.

[0035] Referring now to FIG. 4, a block diagram of a clutter cancellation circuit 400 for a radar in accordance with one embodiment of the present disclosure is shown. The clutter cancellation circuit 400 includes an attenuator 402, a signal delay 404 and a phase shifter 406 communicably coupled to one another in any order. Note that the attenuator 402, signal delay 404 and phase shifter 406 configuration illustrated in FIGS. 4 and 5 are non-limiting examples. In some embodiments, an automatic or manual controller 408 may be communicably coupled to the attenuator 402, signal delay 404 or phase shifter 406. The radar has a transmitter 410 communicably coupled to one or more transmitter antennas 412, and a receiver 414 communicably coupled to one or more receiver antennas 416. One or more clutter cancellation circuits 400 are communicably coupled between a transmission path 418 from the transmitter 410 to the one or more transmitter antennas 412 using a signal splitter 420 or other suitable component, and a reception path 422 from the one or more receiver antennas 416 to the receiver 414 using a signal combiner 420 or other suitable component.

[0036] The attenuator 402 is configured to attenuate a radar transmission signal 422 received from the signal splitter 420. The signal delay 404 is configured to delay the received radar transmission signal 422. The phase shifter 406 is configured to the phase shift the received radar transmission signal 422. The attenuator 402, signal delay 404 and phase shifter 406 are configured to generate a cancellation signal 424, which is combined with a radar return signal in the reception path 422 using the signal combiner 420. The radar return signal contains one or more target signals and one or more clutter signals. The clutter cancellation signal 424 substantially cancels out the one or more clutter signals. The clutter canceller 400 may include additional components. Moreover,additional components may be placed between the one or more transmitter antennas 414 and the attenuator 402, and the phase shifter 406 and the one or more receiver antennas 418. Furthermore, the system may include multiple clutter cancellers 400 that generate different cancellation signals 416.

[0037] In one aspect, one or more of the attenuator, the signal delay and the phase shifter are manually or automatically adjusted or tuned using a controller. In another aspect, the attenuator attenuates the radar transmission signal by an attenuation factor a —the signal delay delays2 p _ the radar transmission signal by a time delay IdAC= where PRX(:is a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light. In another aspect, a power of the signals received from a target and the clutter is PRXa transmit power, GTXis a transmit antenna gain, GRXis a receive antenna gain, o is a radar cross section (RCS), X is a free space wavelength, and R is a distance. In another aspect, the cancellation signal operates in the radio frequency domain. In another aspect, the attenuator operates within a 2-18 GHz range, and the phase shifter operates within a de- 18 GHz range. In another aspect, the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters. In another aspect, the cancellation signal improves the resolution and detection accuracy of a radar. In another aspect, the cancellation signal is effective when a target is stationary or moving.

[0038] In order to verify the theory behind the disclosed clutter cancellation technique, a simplified experiment is developed. The experimental setup uses an FMCW radar system developed in

[0019] , which leverages an Analog Devices HMC358 VCO alongside variable microwave passive components to realize a manually tunable system. The experimental radar system alongside the feedforward components are shown in FIG. 5 with a corresponding block diagram. At the transmit port 502 of the radar 500, the chirp signal is evenly divided into the antenna path 504 and feedforward path 506. The antenna path 502 is connected directly to a 2 x 2 horizontally polarized patch antenna array 508 with a gain of 5 dBi, an effective aperture of 6.28 cm2, and a 3-dB beamwidth of 20°, which will radiate energy into the environment, while the feedforward path 506 consists of 1.8 m of transmission lines 510 to realize the necessary time delay.

[0039] In addition, a 2-18-GHz variable attenuator 512 and de to 18-GHz phase shifter 514 in the feedforward path 506 provide fine amplitude and delay adjustments to precisely match the response of the target 516 and set the bandwidth of the cancellation path to 16 GHz. Backscattered energy from targets 516 and clutter 518 are detected by another 2 x 2 patch antenna array 520 at the receiver 522 and is combined with the output of the feedforward path 524 after delay and attenuation. The feedforward attenuation and fine time delay are then adjusted manually after placing a clutter to minimize its response in the baseband spectrum. In a practical system, however, this can be accomplished using an electronic attenuator and phase shifter to remove the manual adjustment step. If the delay and attenuation are precisely adjusted to provide destructive interference throughout the chirp, the cancellation of the clutter signal occurs at the receive port, negating its impact on a purely analog fashion at the RF front end. As such, it is expected that the impacts of clutter on target detection and range resolution will be completely removed, allowing for accurate target range measurements in the presence of clutter.

[0040] The FMCW radar from

[0019] is driven with a sawtooth signal creating a chirp that occupies a bandwidth from 5.65 to 6.25 GHz (600-MHz bandwidth) with a repetition frequency of 1 kHz. To quantify the impact of the cancellation signal on the sensor’s performance, baseline measurements are first taken without the cancellation hardware and then repeated with the feedforward cancellation path enabled. The measurements taken include a comer reflector 1.65 m from the radar acting as a piece of clutter, a second, smaller corner reflector 1.5 m from the radar acting as the target, and the response with both the target and clutter at their respective locations approximately normal to the plane of the radar antennas with slight offsets to prevent obscuring the target or clutter. FIG. 5 provides an image of the experimental setup used to provide feedforward cancellation, in addition to the locations of the target and clutter reflectors in the sensor’s field of view. The resulting range spectra from the measurements are illustrated in FIG. 6 alongside the ground truths for the clutter and target locations. Before the cancellation loop is enabled, the range spectrum with both target and clutter 602 (solid black curve) cannot resolve the target or clutter ranges, limiting the accuracy and range resolution of measurements near strong static clutter. It is seen that the measurement before cancellation 602 very nearly matches the sum of the measurement with clutter only 604 (blue dotted-dashed curve) and the measurement with target only 606 (green dotted curve), illustrating the impact of limited range resolution on measurements near clutter. The distances to the target 610 and clutter 612 are denoted by the vertical gray lines. After enabling the feedforward cancellation loop, the newspectrum with both the target and clutter 608 (red dashed curve) can effectively resolve the target’s true location despite the presence of clutter near the target. In addition, the measurement almost exactly matches the response of the target-only case, demonstrating that feedforward cancellation can remove the impacts of clutter in such a way that a target can be measured and resolved as if no clutter were present. As such, the proposed technique is shown to improve accuracy, range resolution, and detection ability for FMCW radars using simple signal processing techniques. Using the current system, however, only a single clutter can be canceled, and an increase in clutter distance would proportionally increase the length of the delay line required, limiting the practical applicability of the system. As such, in order to provide enhanced versatility, future systems using this technique could include multiple cancellation paths and software- controlled board-level time delays instead of transmission lines in order to negate these limitations.

[0041] Referring now to FIG. 7, a method 700 for generating a clutter cancellation signal in accordance with one embodiment of the present disclosure is shown. A radar transmission signal is generated by a radar transmitter and received at a clutter cancellation circuit in block 702. The clutter cancellation circuit generates a clutter cancellation signal in block 704 by attenuating, delaying and phase shifting the received radar transmission signal using an attenuator, a signal delay, and a phase shifter in any order.

[0042] In one aspect, the method further includes combining the clutter cancellation signal with a radar return signal from one or more radar receiver antennas, wherein the radar return signal contains one or more target signals and one or more clutter signals. In another aspect, the clutter cancellation signal substantially cancels out the one or more clutter signals. In another aspect, the method further includes manually or automatically adjusting or tuning one or more of the attenuator, the signal delay and the phase shifter using a controller. In another aspect, the attenuator attenuates the received radar transmission signal by an attenuation factor ld— —P,the signal delay delays the received radar transmission signal by a time delay a = — -, where PTXPRXCis a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light. In another aspect, a power of the signals received from a target and the clutter is PRX — where PTXis a transmit power, GTXis a transmit antenna gain, GRXis areceive antenna gain, a is a radar cross section (RCS), is a free space wavelength, and R is adistance. In another aspect, the cancellation signal operates in the radio frequency domain. In another aspect, the attenuator operates within a 2-18 GHz range and the phase shifter operates within a de- 18 GHz range. In another aspect, the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters. In another aspect, the cancellation signal improves the resolution and detection accuracy of a radar. In another aspect, the cancellation signal is effective when a target is stationary or moving.

[0043] The reconfigurable feedforward clutter-canceling FMCW radar system disclosed herein is presented as a method for stationary clutter removal and range resolution improvement in realistic sensing environments. The system leverages a feedforward signal path to provide time delay and amplitude shifts to cancel the effects of clutter in the RF domain and improve the radar’s range resolution and detection accuracy near clutter. A time-domain FMCW radar simulation demonstrates the effectiveness of a theoretical system leveraging adaptive cancellation to destructively interfere with the clutter signal in the analog domain. An FMCW radar system leveraging feedforward cancellation is tested in an experimental setup, where a combination of delay lines, variable attenuators, and phase shifters creates fine time and amplitude shifts to precisely cancel the effects of clutter. Results show that the system removes the effects of clutter in the radar’s resulting range spectrum providing improved range resolution without increasing the used bandwidth. Furthermore, after cancellation, the response of a target near clutter nearly exactly matches that of a target in an uncluttered environment, demonstrating the effectiveness with which adaptive feedforward cancellation removes clutter effects. The system may include electronically tunable amplitude and time shifts for integration in a complete sensor, as well as the development of a board-level canceller that can automatically cancel stationary clutter effects to adapt to a variety of sensing scenarios.

[0044] All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

[0045] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of“one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[0046] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open- ended and do not exclude additional, unrecited features, elements, components, groups, integers, and / or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and / or steps. In embodiments of any of the compositions and methods provided herein, “comprising” may be replaced with “consisting essentially of’ or “consisting of’. As used herein, the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method / process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), property(ies), method / process steps or limitations )) only. As used herein, the phrase “consisting essentially of’ requires the specified features, elements, components, groups, integers, and / or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and / or steps as well as those that do not materially affect the basic and novel characteristic(s) and / or function of the claimed invention.

[0047] The term “or combinations thereof’ as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof’ is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0048] As used herein, words of approximation such as, without limitation, “about”, “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily beabsolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skill in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

[0049] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

[0050] To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. § 112, U.S.C. § 112 paragraph (f), or equivalent, as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.

[0051] For each of the claims, each dependent claim can depend both from the independent claim and from each of the prior dependent claims for each and every claim so long as the prior claim provides a proper antecedent basis for a claim term or element.

[0052] REFERENCES

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Claims

CLAIMSWhat is claimed is:

1. A method for generating a clutter cancellation signal comprising: receiving, at a clutter cancellation circuit, a radar transmission signal generated by a radar transmitter; and generating, by the clutter cancellation circuit, the clutter cancellation signal by attenuating, delaying and phase shifting the received radar transmission signal using an attenuator, a signal delay, and a phase shifter in any order.

2. The method of claim 1, further comprising combining the clutter cancellation signal with a radar return signal from one or more radar receiver antennas, wherein the radar return signal contains one or more target signals and one or more clutter signals.

3. The method of claim 2, wherein the clutter cancellation signal substantially cancels out the one or more clutter signals.

4. The method of claim 1, further comprising manually or automatically adjusting or tuning one or more of the attenuator, the signal delay and the phase shifter using a controller.

5. The method of claim 1, wherein: the attenuator attenuates the received radar transmission signal by an attenuation factor a — —PRXC -■PTX the signal delay delays the received radar transmission signal by a time delay IdAC— and where PRXcis a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light.

6. The method of claim 5, wherein a power of the signals received from a target and the clutter is PRX=Ptx^< tx^rx<tAwhere PTXis a transmit power, GTXis a transmit antenna gain, GRXis a receive antenna gain, o is a radar cross section (RCS), is a free space wavelength, and R is a distance.

7. The method of claim 1, wherein the cancellation signal operates in the radio frequency domain.

8. The method of claim 1, wherein: the attenuator operates within a 2-18 GHz range; and the phase shifter operates within a dc-18 GHz range.

9. The method of claim 1, wherein the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters.

10. The method of claim 1, wherein the cancellation signal improves the resolution and detection accuracy of a radar.

11. The method of claim 1, wherein the cancellation signal is effective when a target is stationary or moving.

12. A clutter cancellation circuit for a radar, comprising: an attenuator, a signal delay and a phase shifter communicably coupled to one another in any order and configured to receive a radar transmission signal generated by a transmitter of the radar; wherein the attenuator is configured to attenuate the received radar transmission signal, the signal delay is configured to delay the received radar transmission signal, and the phase shifter is configured to phase shift the received radar transmission signal; and wherein the attenuator, the signal delay and the phase shifter are configured to generate a clutter cancellation signal.

13. The clutter cancellation circuit of claim 12, wherein: the clutter cancellation signal is combined with a radar return signal from one or more radar receiver antennas; andthe radar return signal contains one or more target signals and one or more clutter signals.

14. The clutter cancellation circuit of claim 13, wherein the clutter cancellation signal substantially cancels out the one or more clutter signals.

15. The clutter cancellation circuit of claim 12, wherein one or more of the attenuator, the signal delay and the phase shifter are manually or automatically adjusted or tuned using a controller.

16. The clutter cancellation circuit of claim 12, wherein: the attenuator attenuates the received radar transmission signal by an attenuation factorPRXCa = —PTX the signal delay delays the received radar transmission signal by a time delay IdAC= and where PRXcisapower received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light.

17. The clutter cancellation circuit of claim 16, wherein a power of the signals received froma target and the clutter is PRX= , where PTXis a transmit power, GTXis a transmitantenna gain, GRXis a receive antenna gain, o is a radar cross section (RCS), is a free space wavelength, and R is a distance.

18. The clutter cancellation circuit of claim 12, wherein the cancellation signal operates in the radio frequency domain.

19. The clutter cancellation circuit of claim 12, wherein: the attenuator operates within a 2-18 GHz range; and the phase shifter operates within a dc-18 GHz range.

20. The clutter cancellation circuit of claim 12, wherein the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters.

21. The clutter cancellation circuit of claim 12, wherein the cancellation signal improves the resolution and detection accuracy of a radar.

22. The clutter cancellation circuit of claim 12, wherein the cancellation signal is effective when a target is stationary or moving.

23. A system comprising: a radar having a transmitter communicably coupled to one or more transmitter antennas, and a receiver communicably coupled to one or more receiver antennas; and one or more clutter cancellation circuits communicably coupled between a transmission path from the transmitter to the one or more transmitter antennas and a reception path from the one or more receiver antennas to the receiver, wherein each clutter cancellation circuit comprises: an attenuator, a signal delay and a phase shifter communicably coupled to one another in any order and configured to receive a radar transmission signal from the transmission path, wherein the attenuator is configured to attenuate the received radar transmission signal from the transmission path, the signal delay is configured to delay the received radar transmission signal, and the phase shifter is configured to phase shift the received radar transmission signal, wherein the attenuator, signal delay and phase shifter are configured to generate a clutter cancellation signal; and wherein the clutter cancellation signal is combined with a radar return signal in the reception path, and the radar return signal contains one or more target signals and one or more clutter signals from the one or more receiver antennas.

24. The system of claim 23, wherein the clutter cancellation signal substantially cancels out the one or more clutter signals.

25. The system of claim 23, wherein one or more of the attenuator, the signal delay and the phase shifter are manually or automatically adjusted or tuned using a controller.

26. The system of claim 23, wherein: the attenuator attenuates the received radar transmission signal by an attenuation factorthe signal delay delays the received radar transmission signal by a time delay ldAC= — ; and where PRXcis a power received from a clutter, Rcis a power received from a clutter distance, and c is the speed of light.

27. The system of claim 26, wherein a power of the signals received from a target and the clutter is PRXPTXis a transmit power, GTXis a transmit antenna gain, GRXis a receive antenna gain, G is a radar cross section (RCS), is a free space wavelength, and R is a distance.

28. The system of claim 23, wherein the cancellation signal operates in the radio frequency domain.

29. The system of claim 23, wherein: the attenuator operates within a 2-18 GHz range; and the phase shifter operates within a dc-18 GHz range.

30. The system of claim 23, wherein the cancellation signal comprises two or more cancellation signals, each cancellation signal generated by different attenuators, signal delays and phase shifters.

31. The system of claim 23, wherein the cancellation signal improves the resolution and detection accuracy of a radar.

32. The system of claim 23, wherein the cancellation signal is effective when a target is stationary or moving.

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