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Radar-based gesture recognition systems are a promising concept for new human–machine interfaces. However, the systems are sensitive to user-dependent gesture patterns, sensor noise characteristics, background environments, and unknown gestures or background motions. To overcome such challenges, we propose a variational autoencoder architecture-based deep metric learning, which is optimized using a novel loss function combining a statistical distance triplet loss and the center loss. By learning the statistical distance between distributions, the proposed solution, compared with triplet loss, is able to better learn the nonlinear characteristics in the data, is less sensitivity to training strategy, and is capable of creating close knit embedding clusters. Moreover, it is experimentally demonstrated that the proposed gesture recognition system using radar spectrograms has improved classification accuracy and random gesture rejection accuracy compared with the state-of-the-art deep metric learning approaches. Furthermore, we proof the real-world capability of the system by implementing a real-time demonstrator, which allows playing “Tetris” with hand gestures. [ABSTRACT FROM AUTHOR]

Identity authentication based on Doppler radar respiration sensing is gaining attention as it requires neither contact nor line of sight and does not give rise to privacy concerns associated with video imaging. Prior research demonstrating the recognition of individuals has been limited to isolated single-subject scenarios. When two equidistant subjects are present, identification is more challenging due to the interference of respiration motion patterns in the reflected radar signal. In this research, respiratory signature separation techniques are functionally combined with machine learning (ML) classifiers for reliable subject identity authentication. An improved version of the dynamic segmentation algorithm (peak search and triangulation) was proposed, which can extract distinguishable airflow profile-related features (exhale area, inhale area, inhale/exhale speed, and breathing depth) for medium-scale experiments of 20 different participants to examine the feasibility of extraction of an individual’s respiratory features from a combined mixture of motions for subjects. Independent component analysis with the joint approximation of diagonalization of eigenmatrices (ICA-JADE) algorithm was employed to isolate individual respiratory signatures from combined mixtures of breathing patterns. The extracted hyperfeature sets were then evaluated by integrating two different popular ML classifiers, k-nearest neighbor (KNN) and support vector machine (SVM), for subject authentication. Accuracies of 97.5% for two-subject experiments and 98.33% for single-subject experiments were achieved, which supersedes the performance of prior reported methods. The proposed identity authentication approach has several potential applications, including security/surveillance, the Internet-of-Things (IoT) applications, virtual reality, and health monitoring. [ABSTRACT FROM AUTHOR]

Compared with a conventional Doppler radar in which target displacement results in phase modulation, target displacement in a self-injection-locked oscillator (SILO)-based radar results in frequency modulation. Since the instantaneous phase is the time integral of frequency, the SILO-based radar is considered to have higher sensitivity than the conventional Doppler radar. However, a direct comparison between the SILO-based radar and the conventional Doppler radar is still needed to quantitatively understand the sensitivity difference. This article provides a rigorous time-domain analysis of the sensitivity of the SILO-based radar with a delay-based frequency demodulator for small-amplitude periodic motions. The analysis follows an approach similar to the time-domain analysis for the conventional Doppler radar. It reveals that two null detection point mechanisms could arise in SILO-based radar systems. The target distance may introduce one null detection point, and the delay added in the frequency demodulator may introduce another. Furthermore, this article also proposes an SILO-based radar with dual null detection points’ removal. Unlike the Doppler radar, where $I/Q$ demodulation eliminates the null detection point introduced by the target distance, $I/Q$ demodulation in the SILO-based radar only eliminates the null detection point introduced by the delay cable. To overcome the other null detection point mechanism, a phase shifter is introduced after the LNA. Experiments were carried out to validate the proposed time-domain analysis and demonstrate that both the techniques need to be used simultaneously to remove both null detection points in the system. The sensitivity comparison was performed using a conventional Doppler radar and an SILO-based radar built with identical microwave components. [ABSTRACT FROM AUTHOR]

A fully polarimetric frequency-wavenumber domain algorithm for 3-D imaging using the synthetic aperture radar technique with irregular sample locations is introduced. At its core, the algorithm works with a multilevel plane-wave representation and relies on some of the concepts of the multilevel fast multipole method (MLFMM). By utilizing a recursive segmentation scheme, the presented algorithm efficiently handles irregular observation locations, which can vary along all three dimensions in space. The basic idea is to divide the observation region into subdomains of decreasing size, until the calculation of the spectral domain representation of the observation data in the individual subdomains by a discrete Fourier transform (DFT) without further acceleration is feasible. The overall uniformly sampled spectral representation of the observation data is then obtained by hierarchical aggregation of the subdomain spectra. The probe influence is fully compensated by the combined processing of several polarizations and solving small linear systems of equations related to the frequency-wavenumber samples on the coarsest level. The focused image is finally computed by fast Fourier transforms (FFTs). This approach, as opposed to conventional coherent back-projection algorithms (BPAs), allows for a fully polarimetric description of the scattering object and achieves good efficiency without loss of accuracy. To show the effectiveness of the algorithm, imaging results obtained from numerical simulations as well as from the evaluation of measured field data are presented and discussed. [ABSTRACT FROM AUTHOR]

A photonics-based leakage cancellation and echo signal de-chirping approach for frequency-modulated continuous-wave radar systems is proposed based on a dual-drive Mach–Zehnder modulator (DD-MZM). The de-chirp reference signal and the leakage cancellation reference signal are combined and applied to the upper arm of the DD-MZM, while the received signal, including the leakage signal and echo signals, is applied to the lower arm of the DD-MZM. When the amplitudes and delays of the leakage cancellation reference signal and the leakage signal are precisely matched, the leakage signal is canceled in the optical domain. The de-chirped signal is obtained after the leakage-free optical signal is detected in a photodetector. An experiment is performed. The cancellation depth of the leakage signal after de-chirping is around 23 dB when the center frequency and bandwidth of the linearly frequency-modulated signal are 11.5 and 2 GHz, respectively. When the leakage cancellation is not employed, the leakage will seriously affect the imaging results and distance measurement accuracy. When the leakage cancellation is enabled, the imaging results of multiple targets can be clearly distinguished, the distance measurement error of a moving target is significantly reduced to less than 10 cm, and a dynamic range increase of 21 dB is achieved. [ABSTRACT FROM AUTHOR]

A novel 4-D gesture sensing technique using reconfigurable virtual array method with a 60-GHz frequency-modulated continuous wave (FMCW) radar is presented. The 4-D sensing includes the 3-D spatial positioning and the 1-D motion tracking, which combines detection in both spatial and temporal domains. The proposed technique can be used for gesture sensing for both macro gestures such as handwriting letters and numbers, hand drawing different patterns in space and micro gestures such as the fingers’ actions of virtual slider, finger tap, and finger wave. Moreover, this work presents a method to reconfigure the working modes of different transmitting and receiving channels in the multiple input and multiple output (MIMO) architecture, which effectively increases the sensing range of the radar sensor and the signal-to-noise ratio (SNR) of the beat signal. For various gestures at different distances or in different environments, the proposed technique can adaptively achieve the best detection by reconstructing the virtual array of the MIMO radar. A series of experiments are carried out in both microwave anechoic chamber and office environments to validate the proposed technique. The experimental results show that the proposed technique performs well in sensing a variety of both macro gestures andmillimeter-level micro gestures. Compared with the conventional MIMO method, the proposed technique increases the sensing range by 3.5 times, and the SNR is also greatly improved by 12 dB when the radar performs gesture sensing at the distance of 0.65 m. [ABSTRACT FROM AUTHOR]

A collocated phased-subarray multiple-input and multiple-output (MIMO) radar system that reduces the number of MIMO channels to implement a large antenna array is proposed. Both the transmitter (TX) and receiver (RX) arrays are divided into phased subarrays, which consist of several RF beamforming antenna elements. Each phased subarray is exploited as an MIMO channel. To estimate the angular information of targets, a hybrid beamforming technique that incorporates RF beamforming of the phased subarrays and digital beamforming of the MIMO virtual array is used. Antenna configurations of the phased-subarray MIMO radar and the corresponding virtual array are also presented. A space between the TX phased subarrays larger than one TX subarray aperture is introduced to facilitate the larger antenna aperture. Because this involves unwanted overall grating lobes, a grating lobe cancellation method is proposed using sum and difference RF subarray beams. This provides a higher angular resolution with the same number of antenna elements. The proposed phased-subarray MIMO radar concept with the corresponding grating lobe cancellation method is demonstrated by implementing a 60-GHz 16-element phased-subarray 2 ${\times }$ 2 MIMO frequency-modulated continuous-wave (FMCW) radar system. [ABSTRACT FROM AUTHOR]

A novel millimeter-Wave (mm-Wave) joint radar and communication (JRC) system based on photonic spectrum-spreading phase-coding is proposed. The key to the proposed system is the convergence of photonic microwave phase-coding and spectrum-spreading multiplexing techniques. Phase-coding enables the generation of wideband mm-Wave JRC signal, leading to both high range resolution (< 3.5 cm) for radar detection and high capacity (>1 Gb/s) for wireless communication. The spectrum-spreading multiplexing orthogonalizes the radar signal and communication data, highly reducing mutual interferences. In addition, the spectrum-spreading multiplexing is able to improve both peak sidelobe ratio (PSR) for radar and anti-jamming/anti-noise performance for communication. In the proof-of-concept experiments, a JRC phase-coding signal at 35 GHz is generated. For a 5-Gb/s coding rate, the signal-to-noise ratio (SNR) margin is improved by around 13.8 dB for wireless communication below the pre-forward error correction (FEC) limit, while the PSR reaches ~12 dB for radar. Moreover, the impact of spreading gain on the communication capacity has been discussed, revealing that an optimized spreading gain should be set to balance the radar and communication performances. [ABSTRACT FROM AUTHOR]

Automotive radars, along with optical sensors such as cameras or lidars, offer a reliable way of obtaining the 3-D information about the environment. Of particular interest in autonomous driving (AD) is the reliable detection of particularly vulnerable road users (VRUs). Modern radar sensors are able to detect, distinguish, and track targets with high resolution. Relying on that, a backscattering model of complex traffic targets can be generated from the reflected signals of their scattering points (SPs). These models can be employed in the radar channel simulations for verification methods of advanced driver assistance systems. Therefore, in this work, different persons as the most vital VRUs are measured with high radial and high angular resolution. The necessary signal processing steps are explained in detail for the determination of the relevant SPs. Thus, the corresponding radar cross section (RCS) values can be assigned to certain body regions. In addition to real persons, further measurements are compared with a dummy of the corresponding size. Based on the measurement results, not only accurate models of road users can be derived, but also the measurement results can be employed for calculating wave propagation in traffic scenarios. From the measured SPs, the classification of the persons by size and stature is derived. [ABSTRACT FROM AUTHOR]

In this work, a method for directly measuring target velocity in three dimensions using a dual axis correlation interferometric radar is presented. Recent advances have shown that the measurement of a target’s angular velocity is possible by correlating the signals measured at spatially diverse aperture locations. By utilizing multiple orthogonal baselines and using conventional Doppler velocity methods to obtain radial velocity, a full 3-D velocity vector can be obtained using only three receive antennas and a single transmitter, without the need for tracking. A 41.8-GHz dual axis interferometric radar with a ${7.26\lambda }$ antenna baseline is presented along with measurements of a target moving parallel to the plane of the radar array, and of a target moving with components of both radial and tangential velocity. These experiments achieved total velocity root-mean-square errors (RMSEs) of 41.01 mm $\cdot \,\,\text{s}^{-1}$ (10.5%) for a target moving along a plane parallel to the array, and 45.07 mm $\cdot \,\,\text{s}^{-1}$ (13.5%) for a target moving with components of radial and tangential motion relative to the array; estimated trajectory angle RMSEs of 10.42° and 5.11° were achieved for each experiment. [ABSTRACT FROM AUTHOR]

The article presents a monostatic $D$ -band frequency-modulated continuous-wave (FMCW) radar based on a fully integrated monostatic single-channel silicon-germanium (SiGe) transceiver (TRX) chip. The chip is fabricated in Infineon’s bipolar-complementary metal–oxide–semiconductor (BiCMOS) production technology B11HFC which offers heterojunction bipolar transistors (HBTs) with an $f_{\mathrm {T}}/f_{\mathrm {max}}$ of 250 GHz/370 GHz. The monolithic microwave integrated circuits (MMICs) output signal is coupled by a fully differential substrate integrated waveguide (SIW) based coupling network. The output power at the WR-6.5 antenna flange is more than −10 dBm over a bandwidth of 37.5 GHz. For a sweep within a single-loop phase-locked loop (PLL) circuit from 174.5 to 121.5 GHz, a spatial resolution of almost 3 mm with a metallic plate as the target is achieved. The radar provides a small form factor of $2 \times 4 \times 5$ cm3 and low power consumption of 2.2 W at 5 V. Finally, the capabilities of the sensor for non-destructive testing (NDT) are demonstrated using a millimeter scanner. With radar imaging, it was possible to measure the orientation of the fiber layers up to a depth of 7.03 mm. [ABSTRACT FROM AUTHOR]

Automotive radar sensors play a key role in the current development of autonomous driving. Their ability to detect objects even under adverse conditions makes them indispensable for environment-sensing tasks in autonomous vehicles. The thorough and in-place validation of radar sensors demands an integrative test system. Radar target simulators (RTSs) are capable of performing over-the-air validation tests by creating artificial radar echoes that are perceived as targets by the radar under test (RuT). Since the authenticity and credibility of these targets are based on the accuracy with which they are generated, their simulated position must be arbitrarily adjustable. In this article, a new approach to synthesize virtual radar targets at an arbitrary angle of arrival (AoA) is presented. The concept is based on the superposition of the returning signals of two adjacent RTS channels. A theoretical model describing the basic principle and its constraints is developed. Additionally, a measurement campaign is conducted that verifies the practical functionality of the proposed scheme. [ABSTRACT FROM AUTHOR]

This work presents a ${D}$ -band monostatic radar system operating from 144.6 to 161 GHz, which is placed inside a 3-D-printed low-cost case with a built-in lens to boost the antenna (ANT) directivity. The monolithic microwave integrated circuit (MMIC) is manufactured in a 130-nm BiCMOS process and includes a compact transceiver architecture consisting of an oscillator, a diode-based mixer, and an on-chip antenna. The implemented topology allows to significantly improve the signal-to-noise ratio and features a built-in self-test (BIST) structure with the possibility to provide on-chip antenna characterization using power sensors in combination with a directional coupler. Housed inside the robust printed package, the MMIC has only dc and baseband frequency connections, which offers ease of handling and poses the low-cost potential for a variety of applications. The complete transceiver chip consumes only 84.7 mA from a 3.3-V supply and its size is 1964 $\mu \text{m}\,\,\times1448\,\,\mu \text{m}$. Together with the package the sensor measures a size of 42.2 mm $\times42.2$ mm $\times45.7$ mm. [ABSTRACT FROM AUTHOR]

With the widespread use of millimeter-wave radar in advanced driver assistance systems (ADASs) and higher level autonomous driving, the probability of mutual interference increases. Radar echoes are distorted by the presence of mutual interferences, leading to the increase of the noise level and even producing ghost targets. Therefore, mitigating interference is one of the most important and pressing challenges for automotive radars today. This article presents an interference mitigation technique in the tunable $Q$ -factor wavelet transform (TQWT) domain. It is discovered that the target’s signal exhibits sparsity in the high $Q$ -factor wavelet transform. Conversely, the interference signal has better representation in the low $Q$ -factor wavelet transform. Then, using morphological components analysis and $l_{1}$ -norm penalized least squares, one sparsity-based nonlinear signal separation model is further derived to reduce the interferences. Finally, the split augmented Lagrangian shrinkage algorithm is applied to optimize the proposed model. Experiments demonstrate that the performance of the proposed algorithm is comparable to three state-of-the-art methods. [ABSTRACT FROM AUTHOR]

A novel matrix-pencil (MP)-based interference mitigation approach for frequency-modulated continuous-wave (FMCW) radars is proposed in this article. The interference-contaminated segment of the beat signal is first cut out, and then, the signal samples in the cutout region are reconstructed by modeling the beat signal as a sum of complex exponentials and using the MP method to estimate their parameters. The efficiency of the proposed approach for the interference with different parameters (i.e., interference duration, signal-to-noise ratio (SNR), and different target scenarios) is investigated by means of numerical simulations. The proposed interference mitigation approach is intensively verified on experimental data. Comparisons of the proposed approach with the zeroing and other beat-frequency interpolation techniques are presented. The results indicate the broad applicability and superiority of the proposed approach, especially in low SNR and long interference duration situations. [ABSTRACT FROM AUTHOR]

We report on the realization of a multichannel imaging radar that achieves uniform 2-D cross-range resolution by means of a linear array of a special form of leaky-wave antennas. The presented aperture concept enables a tradeoff between the available range resolution and a reduction in the number of channels required for a given angular resolution. The antenna front end is integrated within a multichannel radar based on stepped-carrier orthogonal frequency-division modulation, and the advantages and challenges specific to this combination are analyzed with respect to signal processing and a newly developed calibration routine. The system concept is fully implemented and verified in the form of a mobile demonstrator capable of soft real-time 3-D processing. By combining radio frequency (RF) components operating in the $W$ -band (85–105 GHz) with the presented aperture, a 3-D resolution of less than ${1.5}^\circ \times {1.5}^\circ \times $ 15 cm is demonstrated using only eight transmitters and eight receivers. [ABSTRACT FROM AUTHOR]

The improvement of the angular resolution of radar sensors is one of the crucial goals of current radar research. A promising approach to achieve this goal is inspired by the ears of a fly called Ormia ochracea. The working principle was adapted for antennas, and the so-called biomimetic antenna arrays (BMAAs) aroused the interest of several research groups. In this work, BMAAs are incorporated into multiple-input multiple-output (MIMO) arrays, a very common approach of improving the angular resolution, to gain more degrees of freedom in array design. The MIMO BMAAs are modeled utilizing the effective biomimetic antenna distance, a fundamentally new measure introduced in this article to translate the special biomimetic phase progression into a spatial quantity. We present straightforward antenna configurations but also describe how a genetic algorithm can be utilized to optimize both antenna positions and BMAA parameters. The proposed arrays show various beneficial effects such as a wider angular range for unambiguous angle estimation or a narrower beamwidth. The impact of MIMO BMAAs on the angular resolution is thoroughly analyzed both theoretically and by radar measurements in the range of 77 GHz. The measurements confirm the modeling method very well and show a significant increase in the angular separability. [ABSTRACT FROM AUTHOR]

A new method of angle estimation of multiple targets using a distributed interferometric antenna array and wideband space–time modulation generating a dynamic array pattern is presented in this work. Interferometric array measurements of angle of arrival are generally ambiguous in the presence of two or more targets. We propose a new method of mitigating ambiguities in interferometric measurements by multiplying the angle pseudo-spectra from multiple antenna baselines, resulting in detections at only the angles of the targets. Using a single linear frequency-modulated transmitter and a receive interferometric array with $N$ elements, we show a simple and computationally efficient technique to estimate the angle of up to $\mathcal {O}(N^{2})$ targets. We describe the theory behind the technique, present detailed simulations, and provide an experimental verification using a three-element millimeter-wave measurement system. [ABSTRACT FROM AUTHOR]

The trend toward a higher degree of automation in modern cars demands radar sensors providing a significantly increased angular resolution. This is achieved by increasing the number of transmit and receive channels, which is most commonly done by cascading several radar monolithic microwave integrated circuits (MMICs). As for single MMIC radar solutions, the phase noise (PN) contained in the transmit signal is one of the most dominant signal distortions limiting detection sensitivity and range also in cascaded radar systems. In this work, we present a novel method to estimate the mean PN power spectral density (PSD) of two radar MMICs in operation. This estimation result is used to detect whether the frequency-generating circuit of the involved MMICs generate PN out of specification. Different to most of the existing methods, the proposed approach is based on an application relevant frequency modulated continuous wave (FMCW) signal, which is actually used to perform a radar measurement, instead of a continuous wave (CW) signal. Finally, the presented concept is verified based on simulations and with the help of measurement data. [ABSTRACT FROM AUTHOR]

A fast low-cost through-the-wall radar imaging (TWRI) system, based on a vector network analyzer (VNA), a couple of switches and an array of Vivaldi antennas, has been designed, realized, and tested. To solve the TWRI inversion problem, an original theoretical modeling for a class of TWRI techniques whose basic functions are the cross-range Fourier transform (FT) of the scattered field and its covariance operator has been proposed. Using these functions, four conventional algorithms, namely the delay and sum (DAS), the FT, the multiple signal classification (MUSIC), the hybrid DAS-MUSIC and a new algorithm, the hybrid FT-MUSIC, have been derived. All these techniques have been implemented and their accuracy and field of view have been tested on canonical scatterers. Then, the algorithms have been applied to measured data collected in different scenarios constituted by a metallic bar or a human subject in the absence and in the presence of a wall between the antenna and the considered targets. Using the proposed TWRI system, it has been possible to detect a subject located up to 5-m away from the radar antenna array through a tuff wall. The proposed FT-MUSIC algorithm has evidenced performances similar to those of the DAS-MUSIC but with significantly lower execution times. Finally, FT-MUSIC performances in terms of field of view and immunity to disturbances are better compared to those of the MUSIC algorithm. [ABSTRACT FROM AUTHOR]

A radar sensor architecture based on a super-regenerative oscillator (SRO) with very high sensitivity is presented for vital sign detection and motion sensing. As a proof of concept, the proposed SRO-based radar sensor architecture, operating in its logarithmic mode, incorporates a patch antenna as a frequency-selective network to transmit and receive radio frequency (RF) signals at 2.32 GHz to conduct target sensing. In this prototype, a common source heterojunction (HJ)-FET is adopted as a variable-gain amplifier in the positive feedback loop of SRO, where two quench signals, 200 Hz and 10 KHz, are employed respectively at the gate of the transistor to periodically modulate the oscillation condition. Furthermore, the theoretical analysis for the radar signal gain of the proposed SRO radar sensor is carried out, demonstrating a 20 dB/decade voltage gain with respect to the input signal reflected from the target. Thanks to the intrinsic automatic gain control characteristic of SRO, the voltage gain of radar signal can go beyond 100 dB in theory. To this end, the measured voltage gain of radar signals with different quench frequencies of the SRO is compared with the theoretical values in the logarithmic mode, exhibiting a maximum gain of 70 dB in the experiment. In addition, compared with the self-injection-locked (SIL) architecture, the experimental results show that the proposed SRO-based radar sensor can exhibit 34–39 dB voltage gain improvement, thereby detecting the actuator movement and vital sign signals of human target accurately at a longer distance with higher sensitivity and reduced circuit complexity. [ABSTRACT FROM AUTHOR]

This article presents a $W$ -band power amplifier (PA) for automotive radar applications. It was designed in a 28-nm fully depleted silicon-on-insulator CMOS technology with a transition frequency of around 270 GHz and a standard back-end-of-line. The circuit adopts a pseudo-differential topology with coupling transformers, which allow both compact matching networks and layout-optimized interstage interconnections. The power stage exploits a transformer-based folded-cascode structure that is very suitable for low-voltage mm-wave power applications. The PA is able to deliver a saturated output power as high as 13.5 dBm at 77 GHz with a power-added efficiency of 14.5%, while using a power supply as low as 1 V. The linear power gain is 26.5 dB and the current consumption is 150 mA. The PA occupies a core die size of $700\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$. [ABSTRACT FROM AUTHOR]

This article presents the combination of a self-injection-locked (SIL) radar with frequency-modulated continuous-wave (FMCW) and switched phased-array (SPA) techniques to locate multiple people and detect their vital signs with high resolution and high sensitivity. The proposed system utilizes a subharmonic upconverter/downconverter with a 1.675–2.175-GHz chirp local oscillator (LO) signal to convert between a 2.45-GHz SIL IF signal and a 5.8–6.8-GHz FMCW RF signal. It transmits the FMCW RF signal and receives the echo signal using a transmit (Tx) antenna and a switched receive (Rx) antenna array, respectively, and processes the SIL IF signal to produce a range–azimuth map (RAM) that displays the positions of all people, their respiration rates (RRs), and their heart rates (HRs) in the monitoring region. The key advantage of combining the FMCW and SPA techniques is the provision of higher spatial resolution than obtained using each technique alone. This article also proposes a Doppler-weighted RAM to improve the identifiability of the images that are generated by two persons close to each other. Finally, the presented system was experimentally validated by measuring the locations and vital signs of up to five seated persons at a range of more than 1.5 m, of which two persons were seated almost shoulder by shoulder. [ABSTRACT FROM AUTHOR]

We present a novel quasi-circulator (QC)-based monostatic radar MMIC with self-interference suppression. This article concentrates on the proper operation of the radar system, especially in the presence of antenna port mismatch. A relatively high receiver gain of around 28 dB is provided in the RF domain to relax the demand on the IF chain. Thus, antenna port mismatch becomes even more critical as already small levels of TX/RX leakage drive the receiver chain in compression. It can be shown that the measured 14-dB receiver noise figure can be provided even in the presence of a high mismatch. Therefore, detailed analyses according to TX/RX isolation are given based on on-wafer and onboard measurements with different antenna port terminations. In the case of on-wafer measurements, the comparison between on-chip 50- $\Omega $ termination and RF-probe termination is performed. In the case of onboard measurements, the comparison is performed based on a waveguide match, a standard horn antenna, and a high-gain parabolic antenna. Even in the presence of a mismatch of almost 4 dB in the receiver path, the proposed MMIC provides sufficient isolation to avoid any receiver compression effects. Finally, the assessment of the proposed radar MMIC for frequency-modulated continuous-wave (FMCW) application is demonstrated based on an outdoor measurement with a target (7-cm corner reflector) placed in a 100-m distance. Using the parabolic antenna, the SNR of target measurement remains at 25 dB. [ABSTRACT FROM AUTHOR]

This article demonstrates the implementation of 80- and 160-GHz four-channel radar sensors employing the modular scalable platform based on a single relaxed 40-GHz local oscillator and cascadable transceiver chips. The first two channels synthesize $2 \times 2$ multiple-input–multiple-output (MIMO) radar at 80 GHz with onboard $8 \times 1$ patch arrays for enhanced angular resolution, whereas the other two channels employ 160-GHz system-on-chip transceivers with integrated wideband 6-dBi micromachined on-chip antennas for enhanced range resolution. Configurable modulators in each transceiver offer ranging, direction-of-arrival (DoA) estimation, velocity/vibrations measurement, and data communication applications. Frequency-modulated continuous wave (FMCW) is demonstrated with 4-/8-GHz sweep bandwidth at 80/160 GHz corresponding to 3.75-/1.875-cm range resolution. Chirp-sequence FMCW is employed to measure the heartbeat rate of a human, and 78 bpm is measured with 0.06-Hz Doppler resolution. Mechanical vibration rate from a loudspeaker is measured using the CW radar technique, whereas phase-modulated continuous wave is employed for distant selective vibrations measurement. Time-division multiplexing MIMO radar is configured at 80 GHz in a multitarget scenario for DoA estimation, and the targets are distinguished with 25° effective angular resolution. Frequency-division multiplexing MIMO radar technique is demonstrated based on $\Delta \Sigma $ -modulation and binary phase shift keying (BPSK) modulators. Furthermore, the 10-Mb/s BPSK data communication link is evaluated at 80 GHz with a 20-dB signal-to-noise ratio at 1 m. The 160-GHz vector modulators offer additional modulations. [ABSTRACT FROM AUTHOR]

This article describes the wireless and simultaneous interrogation and identification of multiple passive (zero-power) pressure sensors in an industrial environment with a reading range of at least 4 m. The 3-D beamscanning of the scene is performed from a 24-GHz frequency-modulated continuous-wave (FM-CW) radar and for diverse electric field polarizations. The identification is performed using a k-nearest neighbor classification. The benefit of using the cross-polarized electric fields combined with a radar imagery technique is enlightened from the analysis of the background clutter and the simultaneous remote interrogation of several passive pressure sensors at a distance up to 17.7 m. The measurement uncertainty on pressure obtained from the proposed long-range wireless technique is finally reported and discussed. [ABSTRACT FROM AUTHOR]

In modern microwave personnel screening systems, a 2-D synthetic aperture is used to obtain a radar image with resolution limited by the diffraction of electromagnetic waves. Therefore, the antenna system of the screening system has large dimensions, a large number of switched channels, and a high cost, which limits a wider use of these systems, for example, at ground transport hubs or administrative buildings. In this article, we consider a different method of forming synthetic aperture, in which it is formed due to the relative movement of a subject near a stationary antenna system. Using the described experimental setup and imitation experiment with a mannequin, it was shown that the proposed method can significantly reduce the dimensions of a prospective screening system and the number of channels in the antenna system and at the same time obtain detailed radar images of hidden objects. [ABSTRACT FROM AUTHOR]

In order to improve the resolution of imaging radars, electrically large arrays and a high absolute modulation bandwidth are needed. For radar systems with simultaneously high range resolution and very large aperture, the difference in path length at the receiving antennas is a multiple of the range resolution of the radar, in particular for off-boresight angles of the incident wave. Therefore, the radar response of a target measured at the different receiving antennas is distributed over a large number of range cells. This behavior depends on the unknown incident angle of the wave and is, thus, denoted as range-angle coupling. Furthermore, the far-field (FF) condition is no longer fulfilled in short-range applications. Applying conventional signal processing and radar calibration techniques leads to a significant reduction of the resolution capabilities of the array. In this article, the key aspects of radar imaging are discussed when radars with both large aperture size and high absolute bandwidth are employed in short-range applications. Based on an initial mathematical formulation of the physical effects, a correction method and an efficient signal processing chain are proposed, which compensate for errors that occur with conventional beamforming techniques. It is shown by measurements that with an appropriate error correction an improvement of the angular resolution up to a factor of 2.5 is achieved, resulting in an angular resolution below 0.4° with an overall aperture size of nearly 200 $\lambda _{0}$. [ABSTRACT FROM AUTHOR]

The Doppler radar has been widely used in respiration detection. However, most of the existing microwave respiration detection works are intended for either a single human subject in front of the radar or multiple subjects with known positions. In this article, a system based on single-input–multiple-output (SIMO) continuous-wave (CW) radar equipped with adaptive digital beamforming (ADBF) technique is presented to detect the respiration of multiple human subjects at unknown positions simultaneously. A solution based on the modified Capon (m-Capon) direction-of-arrival (DOA) estimation and linear constraint minimal variance (LCMV) ADBF is proposed to automatically find the angles of human subjects. By forming spatially distributed beams toward the subjects of interest, human respiration can be remotely obtained. Furthermore, for the detection of each person’s respiration, nulls are also generated at the angles of nearby interfering subjects, which results in high target discrimination capability when multiple human subjects are close to each other. The experimental results show good detection accuracy compared with the reference sensor, which verifies the effectiveness of the developed system for multitarget respiration detection. [ABSTRACT FROM AUTHOR]

Monostaticmultiple-input–multiple-output (MIMO) radar configurations using the same antenna array for transmission and reception inherently lead to redundant virtual antenna positions within the virtual MIMO aperture. This article presents a new method for designing monostatic MIMO radars where this disadvantage may be overcome and nonredundant virtual arrays are yielded by exploiting biomimetic antenna arrays (BMAAs). The new concept of biomimetic MIMO is introduced and thoroughly investigated in this article. Its working principle is compared with conventional monostatic MIMO and verified by radar measurements. The new approach is intended to improve the angle estimation capability of, in particular, small radar systems. Therefore, the concept is applied to an ultracompact two-channel radar monolithic microwave integrated circuit (MMIC) with fully integrated antennas for range and angle measurements in the 150-GHz range. The chip features two monostatic transmit–receive (TRX) channels with an antenna spacing of $\lambda /4$ and occupies less than 3 mm2 of space. By applying biomimetic MIMO, a virtual aperture consisting of four unique antenna positions and an equivalent total size of around $1.5\lambda $ is achieved. [ABSTRACT FROM AUTHOR]

For highly integrated imaging systems above 100 GHz, the complexity and chip area increase significantly with an increasing number of channels. In addition, bulky dielectric lenses prevent applications in spatially restricted surroundings. The presented concept of an imaging monopulse radar with a mechanically flexible front end reduces the required chip area and allows the antenna to be placed in any desired position apart from the sensitive electronics. The radar system is based on a two-channel 160-GHz microwave monolithic integrated circuit (MMIC) feeding a flexible dielectric waveguide. Depending on the angle of the incidence signal, a sum mode (HE11 mode) and a difference mode (HE21 mode) are excited in the dielectric waveguide. MMIC and waveguide are connected by a self-aligning transition reducing the requirements for packaging accuracy. The required chip area of the transition is only $0.022\lambda ^{2}$ with a spacing between the on-chip antennas of $\lambda /4$. The measured ambiguity-free region between −18° and 15° is defined by the modified elliptical lens antenna focusing in the $E$ -plane only. A mechanical bending of the flexible waveguide is possible down to a radius of at least 2 cm without affecting the angle estimation capability. [ABSTRACT FROM AUTHOR]

Only a few efforts have been made to design small scatterers with special polarimetric properties. In this article, the possibility of designing a planar single-layer resonant scatterer presenting roll-invariant cross polarization is demonstrated for the first time. The invariance condition for a general scatterer is first derived analytically from the scattering matrix for copolarization and cross polarization. Then, a design method for a resonant scatterer made from two dipoles with unique angular and phase arrangement is presented. The first step of the design is done theoretically using field superposition. The effects of the coupling between the dipoles and the finite ground plane size are taken into account in a second step by simulation. Two scatterers operating at 4.26 and 5.26 GHz have been manufactured and measured providing good performance with a relative variation of their cross polarization component lower than −2 and −2.7 dB, respectively. Finally, the scattering matrix corresponding to the current design is compared with other classical targets. [ABSTRACT FROM AUTHOR]

In this article a compact 120-GHz multiple-input-multiple-output (MIMO) imaging radar is presented. With a module size of only 25 cm, an angular resolution of less than 0.9° is obtained in elevation and azimuth direction using 24 transmitters and 24 receivers. The hardware is based on a SiGe:C MMIC technology and integrated into a modular frontend and backend structure. This article presents the overall hardware architecture of the RF-frontend, including a novel reference oscillator distribution concept and a connectorless board-to-board transition based on substrate integrated waveguides. A fully integrated backend is shown, and the entire radar system is evaluated experimentally and the imaging results are presented, demonstrating the large potential of the presented millimeter-wave 3-D imaging radar. [ABSTRACT FROM AUTHOR]

Identifying and locating human targets in a complex environment with a mobile radar platform are important for urban rescue missions. This article introduces a precise phase-based human target 2-D synthetic-aperture radar (SAR) imaging and recognition system based on vital sign tracking with a mobile frequency-modulated continuous-wave (FMCW) radar. The solution first relies on FMCW phase detection to extract the vital sign signal of the human target. It then applies the SAR imaging method to obtain the 2-D imaging of the scene and labels human targets in the detected 2-D map without manual selection. Experiments are carried out for the azimuth human target recognition, multiple human targets recognition, and 2-D mapping in a complex outdoor environment. The results show that the proposed solution can capture not only the vital signs of human subjects but also the precise position information for 2-D mapping, demonstrating great potential for search and rescue applications. [ABSTRACT FROM AUTHOR]

This article proposes a single-conversion stepped-frequency continuous-wave (SCSFCW) radar that combines a stepped-frequency continuous-wave (SFCW) radar and a self-injection-locked (SIL) radar to benefit from the range resolution and the Doppler sensitivity of the two radars. An 8.5–9.5-GHz prototype SCSFCW radar system that comprises a subharmonic up/down converter with a 3–3.5-GHz stepped chirp local-oscillator (LO) signal and a 2.5-GHz SIL IF signal was developed to monitor the vital signs, i.e., respiration rate (RR) and heart rate (HR), of multiple humans. The coherence and range of the developed system were significantly enhanced by using a low pulse repetition frequency (PRF). In the experiment, the minimum distinguishable radial spacing between the vibrating frequencies of the metal plates that are not azimuthally overlapped with one another corresponds to a theoretical range resolution of 15 cm. However, owing to scattering by the human body, the minimum radial spacing for distinguishing between the vital signs of the individuals is three times than that for distinguishing between the metal plates in a similar experimental setup. Accordingly, the monitoring of up to three human vital signs using the developed system was demonstrated with a range-vital-Doppler map. [ABSTRACT FROM AUTHOR]

A new architecture of self-injection-locked (SIL) quadrature radar sensor based on a metamaterial (MTM) leaky-wave antenna (LWA) to detect multi-target vital sign and location simultaneously is proposed for the first time. The angular information of targets is obtained by a 1-D MTM LWA with −50° to +30° beam-steering angle when the frequency varies from 1.85 to 2.85 GHz. Furthermore, the distance from the radar sensor to the targets is obtained by imposing the frequency-shift keying (FSK) modulation on the radar waveforms. Meanwhile, the vital sign signals of multiple targets can be extracted from the Doppler frequency spectrum. For the proof of concept, two frequencies, 2.24 and 2.45 GHz, are chosen to detect two targets at different locations, which correspond to the scanning angle at −10° and −40°, respectively. A first-order microwave differentiator followed by a quadrature coupler is employed to convert the radio frequency (RF) signals from the output of the MTM LWA to in-phase (I) and quadrature (Q) RF signals with frequency-dependent amplitudes, thereby eliminating the null point issues for radar detection. Experimental results show that the proposed SIL MTM radar sensor can detect the target location accurately, while the obtained vital sign results agree well with the ground truth. [ABSTRACT FROM AUTHOR]

This paper describes a software-defined radar sensor based on successive multiple-frequency continuous-wave (S-MFCW) modulation. S-MFCW is a radar modulation technique capable of detecting static and moving targets with high accuracy while modulating the transmitted signal over a narrow frequency bandwidth. The proposed software-defined radar is implemented as a highly reconfigurable system made of a field-programmable gate array (FPGA)-based system-on-chip (SoC), a wideband homodyne radio frequency (RF) transceiver, and two antennas. The utilized programmable general-purpose SoC and transceiver front end allow for some of the radar components to be reconfigured by a software program running on the SoC. This radar system adequately follows the software-defined radar paradigm wherein most of the radar operation is configured and controlled using software programs, thus providing the ability to combine multiple radar functions on the same hardware resource. The presented radar sensor is experimentally evaluated in both outdoor and indoor measurement scenarios. The radar operates in the S-band and occupies a narrow virtual bandwidth of 34 MHz when transmitting S-MFCW tones whose frequencies are shifted by two gaps of 4 and 30 MHz, from 3.550 to 3.584 GHz. Experimental results show that the proposed radar system is capable of measuring short-range targets with a range accuracy of less than 21 cm. [ABSTRACT FROM AUTHOR]

Due to technological advances in various fields and the rising demand for automation, the popularity of service robots is expected to grow rapidly in the upcoming years. One of the core functions of such robots is their interaction with people. One type of interaction, which is studied in this paper, is when the robot leads or follows a person. This presupposes that the position of the person is known relative to the mobile robot. In this paper, we present a 24-GHz wireless locating system to enable this kind of human–robot interaction. The system consists of a radar node attached to the robot and an active portable wireless beacon that is carried by the person. Using a secondary radar approach to measure the distance and angle to the beacon, the 2-D position of the person relative to the mobile robot can be accurately determined by a single radar node on the robot. This is unfeasible with standard multilateration localization approaches. An extended Kalman filter is used to increase the accuracy and reliability of the positioning system. The measurements presented in this paper, performed in a scenario that is both challenging and realistic, demonstrate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A differential phase Doppler radar sensor with multiple receivers (RXs) to remotely detect human vital signals is proposed, which can reduce common motion artifacts as well as common noises to RXs. This is achieved by differentiating two-phase signals from a pair of collocated RXs. Random motions are decomposed into several kinds of motions with respect to the transmitted beam direction. Six differential phase signals are obtained from the four RX combinations, among which at least one pair can get vital signals with reduced common motion artifacts. A weighted-sum method is proposed to combine six differential signals effectively, which allows vital signals to be clearly detected even with large random body motions. A sensor is implemented with a commercially available 24-GHz radar front-end chip with one transmitter and four RXs to verify the differential phase radar concept. An experiment demonstrates that body motion noises are reduced by over 20 dB with the proposed differential phase radar with multiple RXs. [ABSTRACT FROM AUTHOR]

To prevent potential hazards posed by fast-evolving drones, it is of importance to develop a radar system for drone detection. Frequency modulated continuous wave (FMCW) radars are widely used for that purpose. Heterodyne architectures are preferred for them to mitigate dc offset errors. Having said that, FMCW radars suffer from permanent leakage from the transmitter into the receiver. The leakage phase noise raises the total noise floor and limits the radar sensitivity. Here, we propose a stationary point concentration (SPC) technique in order to overcome the challenges. The SPC technique concentrates the leakage phase noise on a stationary point to alleviate the impact of the noise. The technique can be realized using digital signal processing without additional hardware. The results show that the proposed technique significantly lowers the noise floor. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-wideband fully integrated imaging radar at sub-terahertz (sub-THz) frequencies is presented, which demonstrates a fine lateral resolution without using any focal lens/mirror. We have achieved a lateral resolution of 2 mm for an object at 23-cm distance as well as a range resolution of 2.7 mm. To achieve the decent range resolution, in a frequency modulation continuous wave radar configuration, a state-of-the-art chirp bandwidth (BW) of 62.4 GHz at a center frequency of 221.1 GHz is generated and efficiently radiated. We have presented a design technique for the optimal design of the passive embedding around the core transistor to maximize the tuning BW of the voltage controlled oscillator. At the receiver side, to maximize the intermediate frequency level, a subharmonic mixer is utilized, which is designed for the lowest conversion loss. Finally, to obtain the fine lateral resolution, we have implemented near-field beamforming algorithm based on the inverse synthetic aperture radar (ISAR) systems. The synthesized beamwidth is less than 0.5°; hence, high-resolution images are reconstructed. The system is fabricated in a 55-nm BiCMOS process. To the best of our knowledge, this is the first imaging radar at THz/sub-THz frequencies, which utilizes ISAR to achieve a high lateral resolution while the radar system is fully integrated. [ABSTRACT FROM AUTHOR]

This paper suggests the usage of an optimized structure of the embedded wafer-level ball grid array technology for millimeter-wave antennas-in-package. Multiple antenna arrays in a second redistribution layer have been designed, evaluated, and integrated with different transceivers to form very compact sensor packages for 61- and 122-GHz radar applications. The resulting packages contain a complete radar front end while featuring dimensions of $8\,\,\text {mm}\times 8~\text{mm}$. The packages are easy to assemble and replaceable. Theoretical considerations, numerical results, and measurements have been carried out for the single components. For the verification of the sensor packages, a system demonstrator was developed, and measurements have been performed in continuous-wave mode. At both frequencies, promising system performance regarding range and distance errors could be confirmed without the usage of complex processing and calibration algorithms. [ABSTRACT FROM AUTHOR]

Full-coverage synthetic-aperture radar (SAR) imaging and human target identification in complex scenes are very important for security and rescue applications. In this paper, a drone-based vital-SAR-imaging hybrid radar system is proposed to realize targets’ imaging and human identification simultaneously. Carried by an operational custom-built drone with a designed S-shaped trajectory, 2-D SAR images of the entire region could be obtained through the frequency-modulated continuous-wave mode, and the “vital Doppler” effect of human target can be searched through the Doppler mode. Then, the vital-SAR-imaging could be achieved. Several experiments including cart-based SAR imaging with three trajectories, cart-based vital-SAR-imaging, and drone-based multitrajectory vital-SAR-imaging were carried out to reveal the capability and distinct operational features of the proposed system. Experimental results demonstrate that the system has the ability to obtain SAR imaging results in different scenes with multiple trajectories, and the human target could be effectively distinguished from other stationary objects. The results show that the lowest human target location error is 0.06 m in a $4\,\,\text {m} \times 9$ m indoor region, which illustrates the great potential for search and rescue applications. [ABSTRACT FROM AUTHOR]

A multistatic dual frequency continuous-wave radar sensor with separated transmitters and receivers operating at 91.5 and 150.3 GHz is developed and used to monitor particle streams remotely through a dielectric wall. The streams consist of low concentrated multidisperse particles with sizes in the micrometer range. The physical relation between the particle stream’s mass flow and the received signal power is derived and used for calibration. Also, scattering effects are investigated and used to develop a routine for the determination of particle dimensions. In a numerical study, it is shown how a double-bistatic antenna configuration can extend the limits of double-monostatic setups. Also, it is demonstrated how the antennas need to be adapted to the measurement environment to maximize the sensitivity of the radar sensor. Finally, measurement results of the mass loading, velocity, and radius of particles from a multidisperse stream are provided and discussed. [ABSTRACT FROM AUTHOR]

This paper presents a $K$ -band multiple-input-multiple-output (MIMO) radar for short-range localization. This radar features 3-D imaging capability, which can obtain the range, azimuth angle, and zenith angle of a target. The proposed radar system implements the concept of MIMO to synthesize a planar array that realizes 2-D digital beamforming with a small number of transmitter and receiver (T/R) channels. A nonuniformly spaced array configuration is also designed to further reduce the number of T/R channels without sacrificing the beamwidth and sidelobe level. The design principle is detailed in this paper. A prototype with eight transmitter channels and eight receiver channels has been built. A calibration procedure was developed to remove path delays of different MIMO channels. Experiments of the proposed ${K}$ -band MIMO radar prototype reveal its capability in the 3-D localization of multiple targets. This prototype features 7.2° 2-D angular resolution, 90° field of view, −10-dB sidelobe level, and wireless data transfer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A single-pole double-throw antenna switch integrated with a CMOS power amplifier (PA) and a low-noise amplifier (LNA) by using a three-piece transmission line transformer (TLT) for a frequency-modulated interrupted continuous-wave (FMICW) radar front end is presented. The three-piece TLT consists of a PA output TL, an LNA input TL, and a TL connected to an antenna. Parallel switches and $\lambda$ /4 effective impedance transformers are used to provide high isolation. Due to the effective integration, the chip size and overall insertion loss are reduced significantly. The measured results demonstrate that the proposed switch achieves an insertion loss of 2.2 (2.6) dB with an isolation of 33 (33.4) dB in the antenna-to-LNA input (PA output to antenna) direction. The chip, including the PA, LNA, and switch, for a 79-GHz FMICW radar front end is fabricated in 65-nm CMOS technology, and its size is 0.394 mm2. The PA output power is 10.2 dBm at 79 GHz, and the LNA gain is 15 dB at 79 GHz. FMICW radar waveforms are successfully generated with the switch in this chip. The measured results verify that the proposed device generates an FMICW radar waveform at the switching frequency at 6 kHz. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A number of millimeter-wave (mm-wave) integrated radar sensors above 100 GHz were proposed in the past five years. The comparability between these radar systems is limited due to different semiconductor processes, synthesizer topologies, and external periphery. Especially, the issue of using a monostatic or bistatic radar monolithic microwave integrated circuit (MMIC) for single-chip sensors is not discussed in detail. This paper provides a comparison between the different properties of bistatic and monostatic MMICs based on two realized almost identical silicon germanium (SiGe)-MMICs at 154 GHz. In the monostatic case, the influence of the transmit–receive coupler on the performance of the system is explained. In the bistatic case, the illumination of a focusing lens and the leakage from transmitter to receiver are investigated. All properties are verified by measurements. The system performance of the monostatic and bistatic MMIC are compared by the calculated link and noise budget. The detection performance and the signal-to-noise ratio performance are evaluated in two radar measurements. Limitations and suggestions for improvement are given for monostatic and bistatic mm-wave frequency-modulated continuous-wave radar MMICs. [ABSTRACT FROM AUTHOR]

A fully integrated wide-bandwidth transmitter (TX) module intended for use in short-range frequency-modulated continuous-wave radar applications is proposed. By incorporating an on-chip fractional- ${N}$ phase-locked loop based on the fundamental voltage-controlled oscillator, the TX is able to synthesize highly programmable 11-GHz linear chirps around the 65-GHz central frequency, hence theoretically enabling sub-1.5-cm spatial resolutions. Implemented in a 0.13- $\mu \text {m}$ BiCMOS process, the test-chip delivers more than +5 dBm of output power and achieves the measured root-mean-square ramp error (nonlinearity) of 340 kHz for a 60-GHz/ms modulation rate signal over the complete range of interest. The presented TX module dissipates 550mW and also includes an adequate on-board directional $4\times4$ antenna array. [ABSTRACT FROM AUTHOR]