Millimeter-wave Frequency-modulated Continuous-wave Research Articles

Spurs in Millimeter-Wave FMCW Radar System-on-Chip

In this article, we present a nonlinear system model to evaluate the impact of circuit nonlinearities on spurs in millimeter-wave frequency-modulated continuous-wave (FMCW) radar system-on-chips. The developed model includes the harmonics of the frequency multiplier, nonlinearity of the power amplifier (PA) and low-noise amplifier (LNA), the switching operation of the receiver (RX) mixer, the limited bandwidth of the PA, LNA, transmitter (TX) and RX antennas, as well as the TX-to-RX leakage. The developed nonlinear model can be used to derive the frequency and amplitude of spurs in the radar IF spectrum. The major insights about the impact of different nonlinearities and their <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">interactions</i> are as follows. 1) The harmonics of the frequency multiplier appear as spurs in the IF spectrum. 2) The PA can be driven in its nonlinear region to mitigate the harmonics generated by the frequency multiplier. 3) Bandwidth of the TX and RX systems should be limited to attenuate the undesired harmonics. 4) The interaction between the TX-to-RX leakage signal and the LNA nonlinearity can lead to spurs close to the target echo in the IF spectrum.

Characterization of Millimeter-Wave Wideband FMCW Signals Based on a Precisely Synchronized NVNA for Automotive Radar Applications

In this article, a nonlinear vector network analyzer (NVNA) measurement setup is developed to characterize frequency modulated continuous wave (FMCW) signals in the frequency domain. Thanks to the use of precisely synchronized multisine phase reference and pulsed-RF phase calibration standards, such NVNA setup is validated for high-accuracy measurement of wideband FMCW signals at the millimeter-wave test bands. According to the method validation at 24 and 60 GHz with a maximum FMCW bandwidth of 2 GHz, the proposed NVNA setup has lower measurement errors and uncertainties than the commercial real-time oscilloscope (RTO) and vector signal analyzer (VSA), offering a reference standard of test and calibration for automotive radar applications.

A Phased Array Antenna System of a Millimeter-wave FMCW Radar for Blind Spot Detection of Mobile Robots

Mobile robots have been extensively used in manufacturing plants for inter-logistic transportation in recent years. This paper covers a phased array antenna design for a millimeter wave radar system to improve lidar-based navigation systems' safety and environmental consciousness. The K-band phased array antenna, when integrated with 24 GHz Frequency-Modulated-Continuous-Wave (FMCW) radar, not only enhances the accuracy of the 2-D Area Scanning lidar system but also helps with the safe operation of the vehicle. The safety improvement is made by covering blind spots to mitigate collision risks during the rotations. The paper first reviews the system-level details of the 2D lidar sensor and shows the blind spots when integrated into a Mobile Robot prototype. Then continues with the inclusion of an FMCW Low-Speed Ramp radar system and discusses the design details of the proposed K-band antenna array, which will be integrated with a radar sensor.

Estimation of Urine Flow Velocity Using Millimeter-Wave FMCW Radar

This study investigated the feasibility of remotely estimating the urinary flow velocity of a human subject with high accuracy using millimeter-wave radar. Uroflowmetry is a measurement that involves the speed and volume of voided urine to diagnose benign prostatic hyperplasia or bladder abnormalities. Traditionally, the urine velocity during urination has been determined indirectly by analyzing the urine weight during urination. The maximum velocity and urination pattern were then used as a reference to determine the health condition of the prostate and bladder. The traditional uroflowmetry comprises an indirect measurement related to the flow path to the reservoir that causes time delay and water waves that impact the weight. We proposed radar-based uroflowmetry to directly measure the velocity of urine flow, which is more accurate. We exploited Frequency-Modulated Continuous-Wave (FMCW) radar that provides a range-Doppler diagram, allowing extraction of the velocity of a target at a certain range. To verify the proposed method, first, we measured water speed from a water hose using radar and compared it to a calculated value. Next, to emulate the urination scenario, we used a squeezable dummy bladder to create a streamlined water flow in front of the millimeter-wave FMCW radar. We validated the result by concurrently employing the traditional uroflowmetry that is based on a weight sensor to compare the results with the proposed radar-based method. The comparison of the two results confirmed that radar velocity estimation can yield results, confirmed by the traditional method, while demonstrating more detailed features of urination.

Solving Phase Ambiguity in Interferometric Displacement Measurement With Millimeter-Wave FMCW Radar Sensors

The frequency-modulated continuous-wave (FMCW) radar sensor is subject to phase ambiguity in measuring large displacement of over half a wavelength, which is particularly severe in the millimeter-wave FMCW radar sensor due to its short wavelength. The state-of-the-art linear phase demodulation techniques were mostly developed for single tone quadrature continuous-wave (CW) radars such as the Modified differentiate and cross-multiply (MDACM) algorithm. This paper presents a novel linear interferometric displacement measurement technique which can synthesize the quadrature <inline-formula> <tex-math notation="LaTeX">${I}/{Q}$ </tex-math></inline-formula> signals across slow time from a single-channel FMCW radar. In this way, the linear phase demodulation technique developed for the CW radar can now be leveraged for the FMCW radar. The theoretical analysis and working principles are discussed. Exhaustive experiments are performed to validate the proposed technique. It is demonstrated that the displacement motions as large as 10 times of the wavelength can be precisely extracted from a single channel FMCW radar with micrometer accuracy and without any phase ambiguity.

Remote Vital Signs Measurement of Indoor Walking Persons Using mm-Wave FMCW Radar

Research on radar-based non-contact vital sign monitoring systems is critical during the COVID-19 epidemic. The accuracy of remote vital sign measurements has increased with the advancement of radar technology and various algorithms. Most studies require subjects to remain stationary, such as standing, sitting in a chair, or lying on a bed, and various measurement algorithms have been proposed. However, maintaining a stationary state as a prerequisite for measurement limits the development and application prospects of radar-based vital sign monitoring systems. Therefore, this paper presents a novel method for monitoring the vital signs of moving targets using a millimeter-wave frequency-modulated continuous-wave (FMCW) radar. The experimental results showed that regardless of whether the subjects walked at 1 m/s or with the left side of their body facing the radar, the accuracy of the heart rate measurement remained high. In the fixed-route experiments, the root mean squared error (RMSE) for heart rate estimation was 4.09 bpm, with an accuracy of 95.88%.

RaDICaL: A Synchronized FMCW Radar, Depth, IMU and RGB Camera Data Dataset With Low-Level FMCW Radar Signals

Within the autonomous driving community, millimeter-wave frequency-modulated continuous-wave (FMCW) radars are not used to their fullest potential. Classical, hand-designed target detection algorithms are applied in the signal processing chain and the rich contextual information is discarded. This early discarding of information limits what can be applied in algorithms further downstream. In contrast with object detection in camera images, radar has thus been unable to benefit fully from data-driven methods. This work seeks to bridge this gap by providing the community with a diverse, minimally processed FMCW radar dataset that is not only RGB-D (color and depth) aligned but also synchronized with inertial measurement unit (IMU) measurements in the presence of ego-motion. Moreover, having time-synchronized measurements allow for verification, automated or assisted labelling of the radar data, and opens the door for novel methods of fusing the data from a variety of sensors. We present a system that could be built with accessible, off-the-shelf components within a $1000 budget and an accompanying dataset consisting of diverse scenes spanning indoor, urban and highway driving. Finally, we demonstrated the ability to go beyond classical radar object detection with our dataset with a classification accuracy of 85.1% using the low-level radar signals captured by our system, supporting our argument that there is value in retaining the information discarded by current radar pipelines.

Low-cost distance-spoofing attack on FMCW radar and its feasibility study on countermeasure

In this paper, we present a low-cost distance-spoofing attack on a millimeter-wave frequency-modulated continuous wave (FMCW) radar. It uses only a replica radar chipset and a single compact microcontroller board in mass production. No expensive and bulky test instrument is required; hence, a low-cost and lightweight attack setup is developed. Despite the limited hardware resources used in this setup, the replica radar can be precisely synchronized with the target radar for distance spoofing. A half-chirp modulation scheme enables timing compensation between crystal oscillators on the replica and the target radar boards. A two-step delay insertion scheme precisely controls the relative delay difference between two radars at nanosecond order; consequently, the attacker can manipulate the distance measured at the target radar with only a $$\pm \,10$$ m ranging error. Moreover, the feasibility of spoofing attacks on a conventional countermeasure employing random-chirp modulation is discussed. Simulation-based experiments reveal that the attack occurs successfully by estimating the random chirp pattern. This demonstrates the potential feasibility of low-cost malicious attacks on commercial FMCW radar as a physical security threat.

Human Presence Sensing and Gesture Recognition for Smart Home Applications With Moving and Stationary Clutter Suppression Using a 60-GHz Digital Beamforming FMCW Radar

With the advancement of radio frequency (RF) assisted smart home technology, it is critical for the RF sensors deployed indoors to isolate the target of interest from unwanted clutter sources. This paper presents a novel method for suppressing both moving and stationary clutters in an indoor environment to localize stationary human subjects with a millimeter-wave frequency-modulated continuous-wave (FMCW) radar. The method derives its roots from the intrinsic high-pass filter (HPF) characteristic of the exponential moving average (EMA) algorithm, a preferred approach for background stationary clutter suppression. In this work, emphasis was laid on expanding the capability to detect and suppress unwanted moving clutter sources in the indoor environment along with stationary clutters, which has not been widely explored before. The proposed method removes motion artifacts so that the characteristic respiratory signal can be identified for human-aware localization. The paper provides experimental validation of the proposed method, wherein a 60-GHz FMCW radar with digital beamforming (DBF) capability was used to identify the 2-D location of a sitting human subject, with a moving window curtain in the background acting as a strong moving clutter source along with other stationary clutters. In addition, a lateral hand gesture recognition technique is presented, wherein the EMA algorithm was used to enhance the signature of the hand motion. The instantaneous position of the hand at the beginning and end of the gesture was determined to classify the gesture as a left-to-right or right-to-left hand swipe.

On-Chip Antenna Integration for Millimeter-Wave Single-Chip FMCW Radar, Providing High Efficiency and Isolation

A complete functional 60-GHz BiCMOS single-chip millimeter-wave frequency-modulated continuous wave (FMCW) radar with on-chip integrated antennas is designed, realized, and experimentally validated. The chip is configured with one transmitting and two receiving antennas. A high antenna efficiency and isolation between the transmitting and receiving antennas is achieved by using a cavity-backed on-chip monopole and by optimizing the package environment. Surface-wave losses and back radiation are reduced, and a high antenna gain is obtained with small ripples in the antenna pattern by implementing special structures on the PCB of the integrated circuit package. The experimental results from the single-chip radar show that the on-chip antennas provide a gain of 2 dBi with very low back radiation. The realized antennas achieve an impedance bandwidth of more than 50% with a corresponding simulated efficiency of 45%. In addition, the proposed approach suppresses surface waves and meets the specific FMCW radar requirements, such as a more than 25-dB isolation between the transmitting and receiving antennas.

Broadband Frequency-Modulated Continuous-Wave Signal Generation by Optical Modulation Technique

Optical frequency-modulated continuous-wave (FM-CW) signal generation with a bandwidth of 35 GHz and a pulse duration of 1 $\mu$ s in the range of 75–110 GHz is demonstrated with an optical frequency multiplier consisting of an optical modulator and optical filters. The FM-CW signal generator is used as a signal source for the surveillance of obstacles and debris in a large area by a distributed radar system connected to the optical fiber network. The system for millimeter-wave FM-CW signal generation is realized using the functions of a multi-frequency band and segmentation of the radar heads with several channels to avoid radio-frequency interference. The wavelength-division multiplexing technology with simple optical heterodyning aids in realizing these functions with high availability.

Waveform-Diversity-Based Millimeter-Wave UAV SAR Remote Sensing

To integrate a synthetic aperture radar (SAR) into an operational unmanned airborne vehicle (UAV), it should be as small as possible to meet stringent limitations of size, weight, and power consumption. It appears that the novel combination of millimeter-wave frequency-modulated continuous-wave (FMCW) technology and SAR techniques can provide an optimal solution. However, some efficient techniques should be applied to resolve range/Doppler ambiguities in FMCW UAV SAR systems. As such, a technique of waveform-diversity-based millimeter-wave UAV SAR imaging is presented in this paper. Along with the described system concept and signal model, the performance of the diversified waveforms evaluated by their cross correlations is detailed. As the conventional stop-and-go approximation is not valid for FMCW SAR, a modified wavenumber-domain algorithm with a consideration of continuous antenna motion during transmission and reception is derived. This imaging algorithm is validated with computer simulations. Furthermore, one parallel direct-digital-synthesizer-driven phase-locked-loop synthesizer with adaptive nonlinearity compensation, which has been validated by the experimental results, is proposed to obtain a millimeter-wave FMCW signal with fine frequency linearity.