Frequency-modulated Continuous-wave Radar System Research Articles

A Low-Complexity FMCW Surveillance Radar Algorithm Using Two Random Beat Signals.

This paper proposes a low-complexity frequency-modulated continuous wave (FMCW) surveillance radar algorithm using random dual chirps in order to overcome the blind-speed problem and reduce the computational complexity. In surveillance radar algorithm, the most widely used moving target indicator (MTI) algorithm is proposed to effectively remove clutter. However, the MTI algorithm has a so-called ‘blind-speed problem’ that cannot detect a target of a specific velocity. In this paper, we try to solve the blind-speed problem of MTI algorithm by randomly selecting two beat signals selected for MTI for each frame. To further reduce the redundant complexity, the proposed algorithm first performs one-dimensional fast Fourier transform (FFT) for range detection and performs multidimensional FFT only when it is determined that a target exists at each frame. The simulation results show that despite low complexity, the proposed algorithm detects moving targets well by avoiding the problem of blind speed. Furthermore, the effectiveness of the proposed algorithm was verified by performing an experiment using the FMCW radar system in a real environment.

A Compact Integration of a 77 GHz FMCW Radar System Using CMOS Transmitter and Receiver Adopting On-Chip Monopole Feeder

This paper presents 77-GHz CMOS radar transmitter and receiver chips equipped with monopole feeders for use in frequency-modulated continuous-wave radar systems. The on-chip monopole feeder can feed not only the aperture of waveguides but also the slots on planar circuits by simply attaching the chips to a printed circuit board using a low-cost non-conductive epoxy. With the aid of a high ratio multiplier and the proposed on-chip feeder, a radar system can easily be integrated without needing to use precise and expensive millimeter-wave packaging technologies. In order to experimentally confirm this, the chips integrated with waveguides are first measured and a full radar system integrated on the planar circuit is evaluated using the microstrip patch antennas. Finally, with the benefit of compact integration technology, the design of a five-channel 3-D environmental sensing radar for small-unmanned aerial vehicles is presented.

Mobile Radar Mapping—Subcentimeter SAR Imaging of Roads

In this paper, we present a strategy for focusing ultrahigh-resolution synthetic aperture radar (SAR) data for mobile radar mapping. We illustrate the related theoretical background and required extensions on the imaging method based on backprojection techniques. The influence of potential errors in estimating a correct geometry with respect to the imaging quality is investigated in detail by point target simulations. As backprojection techniques require precise knowledge of the topography in close range, the new strategy instantly uses the GPS/INS data of the trajectory to define a suitable digital elevation model of the illuminated scene. We have tested the strategy by driving on conventional roads with an active frequency-modulated continuous wave radar system operating at 300 GHz. Different reference targets were placed in the scene, and the accuracy of the method was evaluated. The results experimentally reveal that the lower terahertz band is capable of subcentimeter SAR imaging in mobile mapping scenarios at very high quality. We have shown that narrow cracks in the asphalt of roads can be detected and fine-scale objects on millimeter size can be displayed. Geometric distortions in the SAR images are significantly reduced allowing the measurements of infrastructure. The output data can at last be transferred to the conventional 3-D Point Cloud Software for further processing.

Feature-Based Hand Gesture Recognition Using an FMCW Radar and its Temporal Feature Analysis

In this paper, feature-based gesture recognition in a frequency modulated continuous wave (FMCW) radar system is introduced. We obtain a range-Doppler map (RDM) from raw signals of FMCW radar and generate a variety of features from the RDM. The features are broadly defined to reflect radar-specific characteristics as well as statistical values commonly used in machine learning. Among these radar features, those that are highly correlated with gesture recognition are selected by the proposed feature selection algorithm, which is a wrapper-based feature selection algorithm incorporated with a quantum-inspired evolutionary algorithm (QEA). Furthermore, the information factor based on the minimum redundancy maximum relevance criterion is applied to QEA in order to find feature subsets effectively. The proposed algorithm is able to extract from all feature sets feature subsets related to gesture recognition, and improves the gesture recognition accuracy of the FMCW radar system. In addition, we analyze which features of the radar are helpful for gesture recognition and perform effective gesture recognition using the features determined through feature analysis.

FMCW multiple‐input multiple‐output radar with iterative adaptive beamforming

This work presents the design of a frequency modulated continuous wave (FMCW) multiple-input multiple-output radar system with collocated antennas. A key part of this article is the modification and application of the iterative adaptive algorithm (IAA) for digital beamforming to an FMCW radar system. The implemented system operates in the 2.4 GHz Industry, Scientific and Medical band with 100 MHz of bandwidth and consists of a transmit (TX) site with four antennas and a receive (RX) site with four antennas. The angular resolution is greatly improved from 15° with the common delay-and-sum beamforming to only 5° with IAA beamforming, which was verified by the results from a radar simulator and by a field test with the implemented hardware. The challenge of synchronisation and maintaining phase coherence in systems with remote TX and RX sites is also addressed by proposing a low-frequency clock and trigger distribution system. This approach allows for cost-efficient systems which can be distributed over longer distances.

An X-Band Frequency-Modulated Continuous-Wave Radar Sensor System With a Single-Antenna Interface for Ranging Applications

In this paper, a highly integrated frequency-modulated continuous-wave (FMCW) radar system with a single-antenna interface for range sensing is proposed. In this paper, a circulator structure was developed and used in the radar system with the single-antenna interface. This structure capitalizes on frequency orthogonality to separate transmitted and received signals; thus, the isolation can be improved by using integrated filters to further suppress transmitter leakage. Without an additional back-end leakage cancellation mechanism and antenna tuner, the single-antenna FMCW radar system can be devised. The proposed system is composed of a radar transceiver, a frequency synthesizer, an analog signal processor, and an AD converter; the system is fabricated using a 65-nm CMOS technology, occupies a chip area of 1.9 mm2, and consumes 147-mW dc power under a 1.2-V power supply. The implemented front-end circuit can provide an output power of 10.5 dBm with power efficiency of 30%, over 1-GHz impedance matching, an insertion loss of 2 dB, a maximum noise figure of 16.8 dB (including the following IF amplifier), $P_{1\,\text {dB}}$ of 2 dBm, and IIP3 of 7 dBm. A wireless measurement process proved that the system can provide a 37-cm range resolution over a 50-m range for a $20 \times 20$ cm2 copper plate. Finally, an FMCW radar front-end board and a digital signal processing board were implemented for data analysis, thus completing the FMCW radar sensor unit. The proposed system can be utilized for multiple applications including 1-D object tracking, 2-D localization, and 3-D object tracking.

Design of a 24 GHz FMCW radar system based on sub‐harmonic generation

This study presents a novel frequency modulated continuous wave (FMCW) radar system based on sub-harmonic generation, where a 24 GHz frequency divider-by-10 is used as an active reflector tag. A practical prototype is designed and fabricated on a GF45nm-Silicon on Insulator (SOI) technology for the 24 GHz building blocks, while a GF0.18 µm 7WL Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) technology was used for the 2.4 GHz receiver and baseband. System measurement results show that as opposed to conventional primary radars, the proposed system is immune to strong multi-path interferences resulting from direct reflections of the interrogating signal. The system achieves a ranging precision of 3.7 mm with loop measurements. Moreover, when measured in an indoor environment, the ranging results show a ranging precision and accuracy of 5.8 and 22.3 cm, respectively, which outperform other FMCW radars in the literature.

Highly Efficient Environment for FMCW Radar Phase Noise Simulations in IF Domain

One of the most dominant signal distortions in a frequency modulated continuous wave (FMCW) radar system is the phase noise (PN) contained in the transmit signal. It has significant impact on the detection sensitivity and range. In this brief, we present a system simulator that directly generates the intermediate frequency (IF) signal of an FMCW radar system, without any computations in the radio frequency (RF) domain. Thus, the simulation can be performed up to about 30 times faster than a corresponding RF simulation, for an arbitrarily shaped input PN power spectral density (PSD). As a major contribution of this brief, an analytical expression for the average PSD of the residual cyclostationary part of the IF signal, which depends on the so-called decorrelated phase noise, is derived. Finally, the simulations are compared with the analytical average PSD as well as with measurement results, and excellent conformance can be observed.

Atmospheric Humidity Sounding Using Differential Absorption Radar Near 183 GHz

A tunable G-band frequency-modulated continuous-wave radar system has been developed and used to perform differential absorption atmospheric humidity measurements for the first time. The radar’s transmitter uses high- power-handling GaAs Schottky diodes to generate between 15–23 dBm over a 10-GHz bandwidth near 183 GHz. By virtue of a high-isolation circular polarization duplexer, the monostatic radar’s receiver maintains a noise figure of about 7 dB even while the transmitter is on. With an antenna gain of 40 dB, high-SNR detection of light rain is achieved out to several hundred meters distance. Owing to the strong spectral dependence of the atmospheric absorption over the upper flank of the 183-GHz water absorption line, range-resolved measurements of absolute humidity can be obtained by ratioing the rain echoes over both range and frequency. Absorption measurements obtained are consistent with models of atmospheric millimeter-wave attenuation, and they demonstrate a new method for improving the accuracy of humidity measurements inside of clouds.

W-Band MIMO FMCW Radar System With Simultaneous Transmission of Orthogonal Waveforms for High-Resolution Imaging

This paper presents a multi-input multi-output (MIMO) radar with simultaneously transmitted orthogonal waveforms. The radar operates in W-band, 93.5–94.5 GHz, with frequency-modulated continuous wave (FMCW) signals. The radar is designed to be capable of simultaneous transmission rather than switching transmit channels. A suitable orthogonal waveform transmission method for the FMCW radar is selected and reflected in the transceiver design. The radar consists of a transceiver, antennas, and a signal processor. The design and specifications of each module are described in detail. The transceiver consists of two transmitting channels and two receiving channels. The transmitter is designed to have high transmit power aiming at the detection and imaging of objects with small radar cross section, up to 100–150-m range. A compact horn antenna and two-channel analog-to-digital converter with a high sampling rate are designed and fabricated. The performance of each module is measured and evaluated. The performance of the radar is tested through experiments. The MIMO capability of the radar was verified through the acquisition of the range profiles with respect to four distinct signal paths by distinguishing the simultaneously transmitted orthogonal signals. The experimental results verified that the specification of the radar system is feasible for high-resolution imaging applications.

FMCW SAR System for Near-Distance Imaging Applications—Practical Considerations and Calibrations

A combination of frequency-modulated continuous-wave (FMCW) technology with a synthetic aperture radar (SAR) technique is a highly sought after method, which leads to a compact and cost-effective imaging system, for near-distance target imaging. One of the limiting factors of FMCW radars is that the ramp signal modulates the received signal, which limits the minimum achievable range resolution. In addition, the voltage-controlled oscillator (VCO) adds a certain degree of phase noise and nonlinearity to the transmitted signal that degrades the signal-to-noise ratio, range accuracy, and image resolution. This paper presents a signal processing procedure with system calibration methods to mitigate the effect of deramp, phase noise, and nonlinearity of the VCO on the beat spectrum. Additionally, the effect of phase noise of the received signal on the SAR image resolution in both range and cross-range directions is comprehensively studied. To improve the range accuracy, different calibration methods are proposed. An $S$ -band homodyne FMCW radar system, using off-the-shelf components, is designed for near-distance target imaging using linear and circular SAR techniques. The reconstructed images show the improvement of image quality and accuracy in target position.

Real-Time Mitigation of Short-Range Leakage in Automotive FMCW Radar Transceivers

Frequency-modulated continuous wave radar systems suffer from permanent leakage of the transmit signal into the receive path. Besides leakage within the radar device itself, an unwanted object placed in front of the antennas causes so-called short-range (SR) leakage. In an automotive application, for instance, it originates from signal reflections of the car’s own bumper. Particularly the residual phase noise of the downconverted SR leakage signal causes a severe degradation of the achievable sensitivity. In an earlier work, we proposed an SR leakage cancellation concept that is feasible for integration in a monolithic microwave integrated circuit. In this brief, we present a hardware prototype that holistically proves our concept with discrete components. The fundamental theory and properties of the concept are proven with measurements. Further, we propose a digital design for real-time operation of the cancellation algorithm on a field programmable gate array. Ultimately, by employing measurements with a bumper mounted in front of the antennas, we show that the leakage canceller significantly improves the sensitivity of the radar.

Implementation of antenna space and beam diversities in a K band FMCW radar system for the short‐range vehicular detections

AbstractThis paper presents the design of a frequency‐modulated continuous wave (FMCW) radar system for the short‐range vehicle detections at K band. The antenna system employs phased arrays to control the radiation patterns to simplify the signal process complexity, which are implemented separately for the transmitter (TX) and receiver (RX), respectively. In particular, the space and angular beam diversities are implemented for RX channels to enhance the detection accuracy. The system is implemented at 24.125 GHz with a bandwidth of 250 MHz, which is used to realize a linear frequency modulation with a TX power of 1 mW. The detection is determined by considering the peak values of signal responses obtained by performing the fast Fourier transform over the signals received by the two RX channels. In this paper, the system architecture is first overviewed, the antenna designs are afterward presented to show their radiation characteristics, and finally, the system is experimentally examined to demonstrate the feasibility.

Gas Flow Monitoring in High and Low Reynolds Regimes Based on Compensated FMCW-Radar Phase Measurements

AbstractIn this contribution, a composite measurement concept for the gas flow determination in diverse stream scenarios is presented. The approach utilizes the pressure- and mixing-dependent relative permittivity of gaseous media, which, in case of a vortex or a marker gas, creates a detectable variation in the measuring beam of the radar. Since the measurement effect is very small, phase measurements based on highly precise and low jitter frequency-modulated continuous-wave radar systems in different frequency bands are applied. Moreover, disturbances caused by vibrations of the measurement setup are compensated out of the measurement signal.

Using Simulations and Computational Analyses to Study a Frequency-Modulated Continuous-Wave Radar

This paper describes a method for simulating Frequency-Modulated Continuous-Wave (FMCW) radar. The developments presented target classroom lectures and can form the basis of student projects. Computational analysis and simulation are critical elements of science and engineering education in which students need to acquire these competencies. FMCW radar system simulations are an example of a real-world application, invested in rich mathematical/physical content that exercise these competencies. Unlike conventional radars that operate in the time domain, FMCW radars operate in the frequency domain. Spectral and phase analyses are required to infer range and the range resolved velocity of meteorological targets such as rain or drizzle. Hence to proceed with simulations, students are first introduced to signals processing topics such as discretization and sampling of signals, Fourier Transforms, Z-transforms, and filters. Computations and the display of results are subsequently performed using Elanix System Vue and Matlab software. To aid the interpretation of the results, a brief description of FMCW physical principles of operation is provided. The computational technique is general and efficient, allowing the range-resolved radial velocity component of precipitation to be computed in real-time. Simulations of range are in excellent agreement with field test measurements of experimental, operational X-band radar currently being evaluated at NASA Goddard Spaceflight Center while computations of the range-resolved velocity component of precipitation agree with the setup conditions of the simulations.

Online Phase-Noise Estimation in FMCW Radar Transceivers Using an Artificial On-Chip Target

The presence of phase noise (PN) severely deteriorates the sensitivity and range of frequency-modulated continuous wave radar systems. Thus, characterization and continuous monitoring of the PN is indispensable, and its estimation is often employed directly on chip. Although many contributions investigate methods for PN estimation, almost all of them consider a continuous-wave (CW) input signal. Differently, in this paper, we aim to estimate the PN from a linear frequency modulated continuous wave (FMCW) signal. For that, we propose two methods utilizing a so-called artificial on-chip target and further digital signal processing. These methods are evaluated in real-time and are the first-known solutions to determine PN estimates during the operation of an FMCW radar transceiver. We prove our methods with both simulation and measurement results from a hardware prototype. Further, we present techniques to efficiently realize the concepts in digital hardware. Finally, we compare and trade off the proposed methods against computational complexity and performance. The novel techniques may be applied to arbitrary input frequencies and bandwidths, and do not require a reference-clock input.

Design and Field Feasibility Evaluation of Distributed-Type 96 GHz FMCW Millimeter-Wave Radar Based on Radio-Over-Fiber and Optical Frequency Multiplier

Foreign object debris (FOD) on airport runways must be removed immediately. To detect small debris, we proposed and developed an optically-connected distributed-type 96 GHz millimeter-wave radar system based on radio-over-fiber (RoF) technology and an optical fiber network. The proposed distributed-type radar system offers both improved FOD detection characteristics and cost performance. This paper details the design and field feasibility evaluation of the 96 GHz frequency-modulated continuous wave radar system that uses RoF and an optical frequency multiplier. Firstly, the problem of long distance RoF transmission, which limits the practical use of the RoF networked radar system in the airport environment, is discussed. Secondly, the concept and architecture of the millimeter-wave radar system are discussed and demonstrated focusing on its use in actual airports. Then, the results of a field experiment are shown to confirm the feasibility of the radar system. Finally, the effectiveness of the high-speed signal processing and generation circuits inside the central unit is evaluated at an actual airport based on the results of non-coherent and coherent signal integration.

Design and development of automotive blind spot detection radar system based on ROI pre-processing scheme

In the conventional 2D-FFT based target detection method, all range-Doppler cells are computed by FFT (Fast Fourier Transform) and scanned by CA-CFAR (Cell-Averaging Constant False Alarm Rate) detection. This results in high computational complexity and long processing time. In this paper, we developed an automotive 24 GHz BSD (Blind Spot Detection) FMCW (Frequency Modulated Continuous Wave) radar with a low complexity target detection architecture based on a ROI (Region Of Interest) pre-processing scheme. In the real BSD zone, because the number of cars to be detected is limited, the designed method only extracts their velocities corresponding to the range ROIs in which real targets exist. Moreover, the presence probability of vehicles with the same range-bin but different velocities is very low. Thus, in the designed method, some Doppler ROIs cells with a high magnitude are only applied for CA-CFAR detection. This architecture can dramatically reduce the amount of data to be processed compared to that of the conventional 2D FFT based method, resulting in enhanced processing time. We developed a 24 GHz FMCW radar system composed a transceiver, antennas, and signal processing module. The designed algorithm was implemented in a tiny micro-processor of the signal processing module. By implementing our proposed algorithm in the developed 24 GHz FMCW radar system in an anechoic chamber and a real road, we verified that the range and velocity of a car occupying the BSD zone were detected. Compared to that of the conventional method, the reduction ratio of the total processing time was measured to be 52.4 %.

Impact of Frequency Ramp Nonlinearity, Phase Noise, and SNR on FMCW Radar Accuracy

One of the main disturbances in a frequency-modulated continuous wave radar system for range measurement is nonlinearity in the frequency ramp. The intermediate frequency (IF) signal and consequently the target range accuracy are dependent on the type of the nonlinearity present in the frequency ramp. Moreover, the type of frequency ramp nonlinearity cannot be directly specified, which makes the problem even more challenging. In this paper, the frequency ramp nonlinearity is investigated with the modified short-time Fourier transform method by using the short-time Chirp-Z transform method with high accuracy. The random and periodic nonlinearities are characterized and their sources are identified as phase noise and spurious. These types of frequency deviations are intentionally increased, and their influence on the linearity and the IF-signal is investigated. The dependence of target range estimation accuracy on the frequency ramp nonlinearity, phase noise, spurious, and signal-to-noise ratio in the IF-signal are described analytically and are verified on the basis of measurements.

A Dual-Band Through-the-Wall Imaging Radar Receiver Using a Reconfigurable High-Pass Filter

A dual-band through-the-wall imaging radar receiver for a frequency-modulated continuous-wave radar system was designed and fabricated. The operating frequency bands of the receiver are S-band (2-4 GHz) and X-band (8-12 GHz). If the target is behind a wall, wall-reflected waves are rejected by a reconfigurable <TEX>$G_m-C$</TEX> high-pass filter. The filter is designed using a high-order admittance synthesis method, and consists of transconductor circuits and capacitors. The cutoff frequency of the filter can be tuned by changing the reference current. The receiver system is fabricated on a printed circuit board using commercial devices. Measurements show 44.3 dB gain and 3.7 dB noise figure for the S-band input, and 58 dB gain and 3.02 dB noise figure for the X-band input. The cutoff frequency of the filter can be tuned from 0.7 MHz to 2.4 MHz.