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In this letter, a novel algorithm is proposed to design symbol‐level waveform for dual‐functional radar‐communication (DFRC) systems with low range sidelobe. Different from current schemes design waveform at the block level, a phase response constraint is introduced at the symbol level to provide an additional degree of freedom to decrease the range sidelobe in the pulse compression procedure, which is highly desired in radar systems. In particular, the phase response at the target direction is constrained to be similar to the given reference phase, and the matching error between the designed beampattern and the desired one is minimized subject to the constant modulus constraint. Furthermore, to guarantee the quality of service for communication, constructive interference is exploited at the symbol level for each communication user. An alternating direction method of multipliers algorithm is also proposed to solve the resulting nonconvex optimization problem with tractable subproblems solved sufficiently by the manifold optimization and standard quadratic problem. Numerical simulation results demonstrate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Radar coincidence imaging (RCI) is a high‐resolution radar imaging mode which constructs a temporal spatial stochastic radiation field (TSSRF) and uses the correlation between reference signal and echoes for imaging. The correlation between the reference matrix and the echoes is the main factor affecting the imaging performance. In fact, radar target characteristics cause fluctuations in the radar cross section and variations in the scattering intensity of each resolution element. The latter degrades the correlation between the reference matrix and the echoes, seriously affecting the image reconstruction. This paper designs the waveform based on image entropy under fixed transmitting and receiving arrays. The targets with fluctuating scattering intensity at each resolution element are statistically modelled. Simulation results show this approach can improve the imaging performance and reduce the energy dissipation degree of the target grid. [ABSTRACT FROM AUTHOR]

Conflict game theory is employed to analyze the countermeasure relationship between radar systems and jammers. To address this issue, a novel utility function and a Conflict Power Allocation Game (CPAG) algorithm are introduced for determining the Nash Equilibrium (NE) solution of the game. The utility function enables the calculation of optimal power response functions for both the radar system and the jammer, with the NE solution of the CPAG algorithm obtained through numerical computation. Simulation results demonstrate the convergence of the proposed CPAG algorithm to the NE solution, validating its efficacy. Finally, an analysis of the relationship between the utility function and pricing factors is conducted based on the proposed CPAG algorithm and simulation outcomes.This article introduces a novel utility function and a Conflict Power Allocation Game (CPAG) algorithm to analyze the countermeasure game dynamics between radar and jammer systems. By deriving optimal response functions using the utility function, the Nash Equilibrium (NE) solution of the game is calculated, demonstrating convergence of the CPAG algorithm. Simulation results validate the efficacy of the proposed approach, highlighting the relationship between the utility function and pricing factors. [ABSTRACT FROM AUTHOR]

This paper presents experimental verification results for a finite‐sized array of a simple non‐reciprocal metasurface elements. The metasurface elements consists of ferrite loaded metal patches. Experimental results demonstrate nonreciprocity, achieving isolation exceeding 20 dB at 6.4 GHz in a 2×2 array. Additionally, these findings are compared with simulation results for a 4×4 array to validate its practicality in a finite array setting. [ABSTRACT FROM AUTHOR]

Although radar sensors have been known for their robustness in challenging environmental conditions, they face difficulties in distinguishing between upper structure (US), such as road signs, traffic lights, overpasses, and pedestrian bridges, and forward vehicle (FV). This misclassification can lead to false alarms and unwanted braking events. In this paper, the authors propose a method distinguishing between US and FV at different distances based on change in radar cross section (RCS). The study collects real‐world RCS data from various objects identified as US and FV during road driving scenarios. [ABSTRACT FROM AUTHOR]

This work proposed a novel constant false alarm rate detection method based on Gaussian mixture model (GMM). The main contribution contains two aspects. First, the Gabor wavelet is used to determine the GMM component number. Second, the expression of probability of false alarm is derived based on the GMM parameter. [ABSTRACT FROM AUTHOR]

Hand gesture recognition based on micro‐Doppler (MD) radar has garnered considerable attention from researchers as a potential method for human–computer interaction (HCI). However, two significant challenges, that is, obvious differences in MD map size and lots of redundant information contained in the MD maps, are encountered. Here, a multi‐scale graph‐based hand gesture recognition framework is proposed. First, a MD graph representation method is developed, which is adapted to arbitrary‐sized frames and enables to map the key features in a sparse manner. Then, the multi‐scale information from MD graph is fully extracted for hand gesture recognition. Experimental results show that the proposed framework achieves a state‐of‐the‐art accuracy of 96.73% on the four‐class radar hand gesture dataset, while reducing up to 99% of the redundant information in the MD maps. This framework requires only a little amount of memory storage with good hand gesture recognition capability, demonstrating its high potential in the HCI field. [ABSTRACT FROM AUTHOR]

A 19‐GHz low‐phase‐noise PLL‐frequency synthesizer is presented in this letter that is intended to be used in a K‐band FMCW radar which requires strict phase noise for detecting a small unmanned aerial vehicle. The 17.9 to 19.5‐GHz PLL includes a Darlington cross‐coupled capacitive‐degeneration VCO which presents higher maximum attainable oscillation frequency (ƒtrans) and larger negative transconductance (gm), thus resulting in low phase noise. Manufactured using the SiGe BiCMOS process, the K‐band synthesizer demonstrates −114 dBc/Hz at 1 MHz offset and −138 dBc/Hz at 10 MHz offset from 19.456 GHz locking carrier frequency. [ABSTRACT FROM AUTHOR]

Dual‐function radar and communication (DFRC) have recently received significant attention as an effective way to alleviate spectrum congestion and reduce system costs. Joint transmit beamforming plays a critical role in DFRC systems, as it can effectively reduce mutual interference and improve the performance of both the radar and communication systems. This paper investigates the problem of robust beamforming design with imperfect channel state information (CSI) to ensure communication performance while optimizing radar performance. Considering elliptically bounded CSI errors, the objective function is designed to minimize the radar loss function, which is related to the radar transmit beam pattern, subject to worst‐case signal‐to‐interference‐plus‐noise ratio constraints at each user, which ensure fairness between users. An efficient algorithm based on semidefinite relaxation and the S‐procedure is proposed to solve the non‐convex problem. Simulation results are presented to illustrate the effectiveness of the proposed robust beamforming scheme, which can reduce the impact of channel errors. [ABSTRACT FROM AUTHOR]

This letter proposes a novel parallel sparse nested array and then provides a matrix reconstruction‐based method with three steps, to enhance the performance of direction of arrival (DOA) estimation in practice. The spacings between the closest antennas along x‐ and y‐axes, are coprime and much greater than half‐wavelength in the proposed array, which contributes to efficiently eliminate the mutual coupling and achieve larger aperture with limited physical antennas. By using the oblique projection operator with iteration, the proposed method can employ all items of covariance matrix of the received data to construct a virtual covariance matrix with increased degrees of freedom, for effectively improving angle estimation performance. Then the unique and high‐accuracy DOA estimation is obtained via the coprime‐ness. The simulation results show the superiority of the proposed array and method for DOA estimation in the presence of mutual coupling and limited antennas. [ABSTRACT FROM AUTHOR]

In this letter, a dilating and embedding scheme for constructing sparse multiple-input and multiple-output radar arrays is addressed, which seeks to increase the uniform degrees of freedom (uDOFs) and reduce the mutual coupling effects for a given number of transmitters and receivers (Tx/Rx). According to this scheme, a dilated maximum interelement spacing constraint (MISC) array with an embedded thinned coprime array in the collocated MIMO radar for DOA estimation is proposed. Theoretical analysis shows that the proposed array can provide higher uDOFs and is robust in a scenario with heavy levels of mutual coupling. Numerical simulations are conducted to validate its aforementioned advantages in line with the design scheme. [ABSTRACT FROM AUTHOR]

Specifying parameters of high-speed targets as range and velocity in radar systems operating with phase-modulated signals is a problematic process because of the serious effect of high Doppler frequency on these types of waveforms. In the existence of a high-speed target, its Doppler frequency will be very high such that it totally changes the phase sequence of the received signal. As a result, the matched filter output will be distorted. Therefore, estimating target parameters will be impossible. In this letter, a new method is proposed for detecting and estimating velocity of high speed targets using phase-modulated signals. The suggested technique methodology depends on compensating the target high-Doppler frequency for signal recovery using a customized waveform shape. Moreover, the Doppler frequency value is estimated without ambiguity from one pulse, and without the need for a range-Doppler module. As such, the implementation of the proposed method is simple and inexpensive. The performance evaluation of the new method shows its superiority in compensation and estimation compared to other techniques when examined under higher Doppler frequency and noise compared to the conventional radar. [ABSTRACT FROM AUTHOR]

In this paper, the application of a hybrid representation in wide‐angle synthetic aperture radar (WASAR) imaging is investigated, addressing the challenge of achieving sparse representation in the presence of complex electromagnetic scattering characteristics and highly anisotropic targets. A convolutional neural network is utilized to represent the two‐dimensional data within each azimuth aperture, while employing blind compressed sensing (BCS) to achieve sparse representation across different azimuth apertures. Convolutional neural network (CNN) excels in learning spatial hierarchies and local dependencies of two‐dimensional data but requires a large amount of training data. Isotropic targets within each azimuth aperture can be used for training conventional SAR data, while acquiring training samples for anisotropic targets poses challenges. To address this issue, BCS are integrated into WASAR imaging, eliminating the need for additional training data. By integrating these methods, a novel approach called hybrid‐WASAR is proposed, which incorporates two regularization terms into WASAR imaging and employs the alternating direction method of multipliers to iteratively solve the imaging model. Compared to traditional WASAR imaging techniques, hybrid‐WASAR improves the accuracy of reconstructing the backscattering coefficients of the targets, leading to a significant enhancement in overall imaging quality. [ABSTRACT FROM AUTHOR]

With the advancement of manoeuvrability and the increasement of coherent processing interval (CPI), the observed target might be of multiple motion stages. Therefore, most existing long‐time coherent integration (LTCI) algorithms based on the assumption of single‐motion stage is not proper any more. To address this problem, this letter proposes an effective motion parameters estimation algorithm, which is the key step of LTCI, for the manoeuvring weak target with multiple motion stages based on range symmetry transform and short‐time fractional Fourier transform (RST‐STFrFT). The effectiveness of the proposed algorithm is verified by signal‐level simulations. [ABSTRACT FROM AUTHOR]

This letter proposes an improved synthetic aperture imaging algorithm to enhance the imaging performance in the Azimuth Missing Data (AMD) case. The proposed algorithm designs an effective phase compensation function based on the Range Cell Migration Correction (RCMC) echo and first reconstructs the complete RCMC echo from the AMD echo. The accuracy of echo reconstruction is improved, leading to a better imaging result. Numerical simulations and a real measured experiment verify the effectiveness of the proposed algorithm. Furthermore, since the range positions of targets can be located after RCMC processing, only non‐zero RCMC signals are reconstructed. Thus, the computational complexity superiority of the proposed algorithm is obvious, especially when the targets are sufficiently sparse in the range direction. [ABSTRACT FROM AUTHOR]

Synthetic Aperture Radar (SAR) Coherent Change Detection (CCD) allows for the detection of very small scene changes. This is particularly useful for reconnaissance and surveillance as small changes such as vehicle tracks can be identified. In some situations, it is desirable to rapidly collect repeat pass SAR images for use in change detection, and multistatic geometries may facilitate this. Such repeat passes may however have significant baselines, particularly for satellite‐based platforms, though CCD products are reliant on high coherence for good interpretability. This work investigates the sources and levels of incoherence associated with bistatic SAR imagery with increasing baselines using simulations and measured laboratory data. [ABSTRACT FROM AUTHOR]

This letter proposes an efficient tensor model for Direction of Departure (DOD) and Direction of Arrival (DOA) estimation based on bistatic nested Multiple‐Input Multiple‐Output (MIMO) radar. Tensor offers a robust solution in characterizing multi‐dimensional data structures, ensuring data integrity, and has demonstrated remarkable effectiveness in the realm of multi‐dimensional parameter estimation. However, the complexity of traditional methods for constructing tensors is a major obstacle to practical applications. In response, this research introduces a novel approach that utilizes an iterative two‐dimensional Toeplitz matrix reconstruction method to rapidly derive expanded virtual covariance matrices prior to tensor construction. This streamlines the algorithm and improves efficiency. Numerical simulations have verified the superiority of this algorithm. [ABSTRACT FROM AUTHOR]

The radome can protect the enclosed antenna from harsh weather and environmental conditions; however, it will cause a non‐negligible effect particularly transmission loss on the wideband signal which has been widely used in electronic systems. For this, a novel transmission loss compensation method for radome based on non‐linear frequency modulation (NLFM) waveform design is proposed. First, the transmission coefficient calculation process is given, Then, the detailed NLFM waveform design method is described in detail. Finally, the simulation experiments are demonstrated to verify the effectiveness of the proposed compensation method. Based on the designed NLFM waveform, the transmission loss can be compensated and a flat frequency response can be obtained, which can achieve excellent performance of pulse compression in the range direction. The proposed NLFM design method has great potential application value in the electronic system. [ABSTRACT FROM AUTHOR]

A novel power line detection method exploiting the Bragg point of power line is proposed in this paper. First, the radar echo of power line is divided into multi‐band along the frequency dimensional with incomplete repetition at equal intervals. Then, the candidate power lines in the echo of each frequency band can be found exploiting the Hough transform and constant false alarm rate (CFAR). Since the Bragg angle of the power line will change with frequency while that of the artefacts is fixed, the power lines can be easily detected from the background by exploiting unique frequency feature of Bragg angle of power line. [ABSTRACT FROM AUTHOR]

Synthetic Aperture Radar (SAR) renderings in 3D provide additional target information when compared to 2D by separating out features overlaid in height. However, the required 2D SAR aperture, when Nyquist sampled, necessitates large scanning times that would be impractical for most realistic collections. This research has developed a novel volumetric approach to sparse aperture 3D SAR imaging, which is applicable to bistatic SAR near‐field geometries, a generalization of far‐field cases. This approach is first demonstrated in simulation and then applied to a measured scene containing a model vehicle target, producing sub‐Nyquist sampled 3D SAR renderings. [ABSTRACT FROM AUTHOR]

Interferometric synthetic aperture sonar (InSAS) systems produce high resolution seafloor imagery and 3‐D bathymetry by exploiting the phase differences between image pairs formed from data collected by vertically separated arrays. This process is non‐trivial due to the inherent ambiguity of interferometric phase estimates, and the effect of layover, where the response of multiple scatterers with different positions are mapped onto the same pixel during imaging. These effects are particularly problematic for complex scenes with strong bathymetry, such as ship wrecks. This is an unsolved problem and improved algorithms for InSAS bathymetry estimation are needed. However, developing and assessing such algorithms using data from fielded InSAS systems is difficult because of a lack of accurate ground truth for the platform motion and the true 3‐D shape of the scene. This paper presents an openly available synthetic data set as an alternative to field‐collected data for use by InSAS algorithm developers. The dataset is derived from a high‐resolution 3‐D photogrammetry scan of the SS Thistlegorm wreck. It was produced by a point‐based diffraction model using parameters similar to the Minehunting UUV for Shallow water Covert Littoral Expeditions (MUSCLE) InSAS.This paper introduces an openly available synthetic dataset for the future development, assessment, comparison, and benchmarking of interferometric synthetic aperture sonar (InSAS) algorithms. The simulated InSAS data is from the SS Thistlegorm ship wreck. It has been produced using a 3‐D photogrammetry model of the wreck and a point‐based diffraction model for the coherent underwater acoustics. It presents a significant challenge due to its strong bathymetry and complex layover. [ABSTRACT FROM AUTHOR]

This letter considers the problem of beamforming in multiple‐input multiple‐output (MIMO) radar. The mismatch phenomenon of MIMO radar virtual array steering vector is addressed, which can better describe the mismatch characteristics of not only one‐way transmitting or receiving path but also the whole transmit‐receive path for a collocated MIMO radar. Then, a new robust beamforming method for MIMO radar against virtual array steering vector mismatch is proposed. The object function of this robust MIMO radar beamformer is constructed from an infinite norm of the output data, which is solved by linear programming. The performance of the proposed beamformer is verified by simulation results. Numerical results illustrate that proposed beamformer exhibits good performance improvement in virtual array steering vector mismatch compared to conventional methods. [ABSTRACT FROM AUTHOR]

This letter formulates a high‐dimensional multi‐objective optimization model to minimize all correlation function values for multiple input multiple output (MIMO) radar waveforms. Then, to solve this problem, this letter proposes an adaptive weighted cyclic algorithm‐new (CAN), named p‐norm weighted cyclic algorithm‐new (p‐WeCAN). Specifically, the adaptive weight updating function is constructed using p‐norm to minimize peak side‐lobe level (PSL) and integrated side‐lobe level (ISL) simultaneously. Numerical results show that the p‐norm weighted cyclic algorithm‐new obtains similar PSL values as the best PSL minimization algorithm and low integrated side‐lobe level values close to its lower bound at the same time. [ABSTRACT FROM AUTHOR]

The problem of high‐resolution direction finding is considered using a distributed array network with array position errors, called partly calibrated array. These errors are common in practice, and significantly affect high angular resolution. Existing calibration methods rely on centralized data transmission, which requires all the measurements to be transmitted to a computation center. This centralized mode leads to communication bottlenecks and system inflexibility. Here, a decentralized mode is designed, where each sensor only communicates locally with their neighboring sensors. Based on this mode, a corresponding direction‐finding approach is proposed using sequential methods that process data one by one, which corresponds to the decentralized signal processing sensor by sensor. Simulations verify that the proposed method achieves decentralization with minor cost in estimation accuracy.We consider high‐resolution direction finding using distributed arrays with position errors between subarrays. Existing methods are based on centralized mode, which has communication bottlenecks and system inflexibility. Here, we propose a decentralized algorithm to solve this problem. [ABSTRACT FROM AUTHOR]

Suppressing false alarms without impacting detection rate is an essential issue for search radars. Traditional threshold detection methods identify true targets by simply comparing the energy of target candidates with a threshold. In this work, a new data‐driven false‐alarm suppression approach is proposed based on a random forest model. It discriminates true targets and false alarms in the developed multi‐dimensional ambiguity feature spaces, instead of the time‐frequency features used in previous works, to fulfill short dwell‐time requirement of search radars. Evaluations through field experiments demonstrate that the proposed method can achieve as high as 98% validation accuracy and a significant improvement of detection performance compared to the conventional threshold detection. [ABSTRACT FROM AUTHOR]

In this letter, the jamming resource allocation problem of distributed jammers cooperatively jamming netted radar system is investigated. A well‐constructed jamming resource allocation model considering jamming beams, jamming power and other influencing factors is established. Random keys are used in this letter to improve the coding mode of genetic algorithm. Simulation results show that in the case of limited jamming resources, the model and algorithm proposed can achieve effective jamming allocation schemes facing a netted radar with any number of radar nodes. [ABSTRACT FROM AUTHOR]

With the rapid development of radar, the phenomenon of Doppler frequency shift is not rare. Frequency shift needs to be considered in order to accurately calculate the mutual interference between signals. Meanwhile, to reduce interference to the received signal, each user's frequency hopping sequence shall have wide frequency hopping gap. The authors introduce the time-frequency two-dimensional Hamming correlation function and extend the bounds for wide-gap frequency-hopping sequences. The Li-Fan-Yang-Wang bounds are the special cases of our bounds for frequency shift is zero. [ABSTRACT FROM AUTHOR]

In this paper, a novel method using target movement characteristic is proposed to classify human and vehicle based on low resolution radar system. Many studies have demonstrated the ability of radar micro‐Doppler signature for ground moving targets classification. However, the micro‐Doppler signals are not always observed in practical application. Considering the motion characteristic of human and vehicle, a multi‐frame joint scheme is proposed, in which three suitable features are extracted and the Random Forest classifier is used to identify three kinds of moving targets. The experiment results with satisfied classification accuracy prove that the proposed method is capable of human‐vehicle classification. [ABSTRACT FROM AUTHOR]

To minimise the noise interference in the radar received echoes and optimise the detection issue for a wideband radar system, a novel wideband radar track‐before‐detect detector via Wiener Filter is proposed. The Wiener Filter can effectively remove the noise mixed in the echoes and make the filtered signal consistent with the original signal. After applying maximum likelihood estimation to the echoes, the authors can reconstruct the desired signal required for Wiener filtering by extracting the range information of each scatterer. Then Wiener Filtering is performed on the echo containing noise with the desired signal to complete the denoising. Subsequently, we exploit the correlation between the adjacent echoes for detection. The effectiveness of the detector can be verified by the numerical simulation results of synthetic and real radar data. The proposed detector is superior to the waveform contrast detector, inter‐period correlation processor and modified correlation matrix detector. [ABSTRACT FROM AUTHOR]

In radar detection for micro‐drones, the performance of the characteristics and features of micro‐drones distinctly varies depending on their motion states. Therefore, this study presents an extraction method for spectral signatures of radar cross section (RCS) to classify and discriminate between typical motion states of micro‐drones. The features related to the RCS of the micro‐drones are transformed and converted into a modified Mel frequency cepstral coefficient (MFCC), which is proposed to detailedly characterize the spectral change of RCS along with different movements. Then the hidden Markov model (HMM) is used to recognize the typical movements of micro‐drones based on the modified MFCC. Experiments in X, Ku bands and HH, VV polarization modes are conducted to investigate the effectiveness of the proposed method, and the classification results with average accuracy above 97%$\%$ are also demonstrated in experiments in discriminating between five different motion scenarios of micro‐drone. The works involved will aid in maximizing classification accuracy for micro‐drones in real scenarios and subsequent situation awareness. [ABSTRACT FROM AUTHOR]

This study has been made to improve the detection capacity of radar using phase coded waveforms especially the Golay set sequence while keeping the sidelobe ambiguity function to the possible minimum. This Letter begins with a description of Golay complementary sets construction from a graph and a determination of the parameters on which they depend to be optimised after. Then, the simulated annealing (SA) algorithm has been proposed to deal with low ambiguity problem of the Golay set, due to its simplicity and also to its effectiveness to solve this kind of problem. Simulation results show that the optimisation with SA has impressively improved the sidelobe rejection of Golay set sequences with a gain of up to 20 dB. [ABSTRACT FROM AUTHOR]

In a conventional radar system, the hardware cost increases with the sampling rate of the receiver. Sub‐Nyquist radar systems operate at lower sampling rates and hence reduce the hardware cost and complexity. A sub‐Nyquist radar system uses the knowledge of the transmit pulse shape to determine the targets. However, the pulse shape is often distorted in practice and unknown to the receiver. An alternative sub‐Nyquist radar system that uses multiple receiver was proposed that estimates the targets without knowledge of the pulse shape. In this demo, the authors build a hardware prototype to demonstrate the proposed multi‐receiver sub‐Nyquist radar. The proposed two‐receiver system with an unknown pulse has comparable pre‐forms to a conventional sub‐Nyquist system is shown. This paper shows a hardware demonstration of sub‐Nyquist sampling of finite‐rate‐of‐innovation signals when the basic pulse shape is unknown. The results are particularly interesting in radar imaging, where the transmit pulse is distorted while propagation and unknown at the receiver. [ABSTRACT FROM AUTHOR]

Range ambiguity suppression is a significant problem in traditional pulse‐Doppler radar systems, especially when the pulse repetition frequency is set high to avoid Doppler ambiguity. One possible way to deal with such problem is to apply the noise radar system, by transmitting pulse‐agile waveforms and using a group of matched filters as the receiver to accumulate the power of unambiguous echoes while dispersing the range‐ambiguous ones. However, when strong targets or heavy clutters exist, the dispersed ambiguous power is still high, which leads to high range‐Doppler sidelobes and overwhelms the weak targets. This paper explores a new way to deal with the range‐ambiguity suppression problem in noise radar. The range‐ambiguity suppression as a sparse recovery problem is formulated, and then both the unambiguous and ambiguous targets (and/or clutters) can be simultaneously reconstructed. The proposed method can enhance the range‐ambiguity suppression performance and synthetic an ambiguity‐free range‐Doppler map with a low sidelobe level, which ensures the weak target recovery performance even in a cluttered environment. [ABSTRACT FROM AUTHOR]

Harmonic radar transponders are passive RF tags that produce a harmonic response when illuminated with an RF signal. With a Schottky diode as the main component, the tag current is usually modelled as an exponential function of antenna voltage, resulting in an approximate polynomial function for small signals. The authors introduce the Lambert function that accounts for the resistive load and leads to a two-region tag model: a power series representation for small signals and an asymptotic linear large-signal model. Furthermore, they provide the relationship between the modulated bandpass signals at the input and output of the tag in the two regions by expressing the tag signals with complex envelopes. The derived expressions offer deeper insight of the transponder's impact on the operation of harmonic radar systems. [ABSTRACT FROM AUTHOR]

Fractional-N phase locked loops (PLLs) offer a low-cost solution to the precision frequency ramp requirements of frequency-modulated continuous-wave (FMCW) radar. In this application, however, the infamous spurious signals generated by these PLLs have not received adequate analysis. In this Letter, the authors investigate the impact of integer boundary spurs on FMCW radar performance. They show that the offset of these spurs is swept during the course of waveform generation, and that undesirable spur chirps manifest in the beat signal as a result. These spur chirps span the radar's intermediate frequency bandwidth and produce Fresnel ripples in the range profile which reduce spurious-free dynamic range. They present simulations and measurements that demonstrate how reduction of PLL bandwidth can be used to suppress these spurii. [ABSTRACT FROM AUTHOR]

Synchronisation of radar systems can be used to suppress interference and enable communication between radars. In this paper, a generalised Kuramoto model is proposed, which can be used to synchronise pulse repetition frequencies of two radars over‐the‐air. The generalised approach allows the adjustment of a sampling factor which influences the convergence of the two pulse repetition frequencies. Furthermore, sampling criteria are derived, which can be used to estimate whether convergence occurs. Finally, it is shown by means of simulation that the model together with the criteria allows to reliably predict convergence and to perform synchronisation. [ABSTRACT FROM AUTHOR]

Photonics-based radar enables a large operation bandwidth that is particularly favourable for high-resolution synthetic aperture imaging. However, how to implement fast and high-accuracy imaging with photonics-based broadband radar is still an open question. In this Letter, the performance of photonics-based inverse synthetic aperture radar imaging with frequency-domain and time-domain algorithms are experimentally investigated and compared. The results show that, frequency-domain range–Doppler algorithm has fast imaging capability, but the image suffers from defocusing and distortions. Although migration compensation techniques can be applied to improve the imaging accuracy, the imaging speed is significantly reduced. On the other hand, using time-domain back-projection (BP) algorithm can achieve well-focused images, and the imaging speed can be enhanced with fast BP methods. Therefore, the time-domain imaging method is found to be the best choice for fast and high-accuracy synthetic aperture imaging with photonics-based broadband radars. [ABSTRACT FROM AUTHOR]

An iterative adaptive approach (IAA) based algorithm is presented to realise coherent integration for the random pulse repetition interval radar. The proposed method firstly removes the effect of Doppler ambiguity via phase compensation, and then accomplishes target focusing via conducting the azimuth IAA and range inverse fast Fourier transform. Theoretical analysis and numerical experiments have verified the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

As a typical signal processing problem, direction-of-arrival (DOA) estimation has been adapted to a wide range of applications in radar-based systems. A high DOA resolution requires a large number of antenna elements which increases the overall cost. To minimise the cost, it is desirable to choose an optimum sub-array from a full array. To enable cognition, the subarrays are selected based on the present target scenario. By using deep learning (DL) based techniques, the authors show a cognitive sparse array selection technique. By using hardware simulations, they demonstrate the applicability of the deep learning (DL)-based sparse antenna selection network in direction-of-arrival (DOA) estimation problems. They show that the DL-based sub-arrays lead to a higher direction-of-arrival (DOA) estimation accuracy by 6 dB over random array selection. [ABSTRACT FROM AUTHOR]

Radar sensors have a new growing application area of dynamic hand gesture recognition. Traditionally radar systems are considered to be very large, complex and focused on detecting targets at long ranges. With modern electronics and signal processing it is now possible to create small compact RF sensors that can sense subtle movements over short ranges. For such applications, access to comprehensive databases of signatures is critical to enable the effective training of classification algorithms and to provide a common baseline for benchmarking purposes. This Letter introduces the Dop-NET radar micro-Doppler database and data challenge to the radar and machine learning communities. Dop-NET is a database of radar micro-Doppler signatures that are shareable and distributed with the purpose of improving micro-Doppler classification techniques. A continuous wave 24 GHz radar module is used to capture the first contributions to the Dop-NET database and classification results based on discriminating these hand gestures as shown. [ABSTRACT FROM AUTHOR]

A two-stage target detection approach, jointly performing traditional and approximate message passing (AMP) algorithms, is proposed for linear frequency-modulated continuous-wave radar. In the first stage, fast Fourier transform (FFT) and target pre-detection are carried out. Based on the pre-detection results, a reduced-dimension signal observation model is established. In the second stage, AMP is used to reconstruct true targets, and then target detection is implemented. Performances of the proposed approach are provided by numerical experiments and compared with those of AMP and the traditional FFT-based methods. Results indicate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This Letter addresses the coherent integration problem for the moving target detection in a pulse repetition interval (PRI)-staggered radar system. Due to the random sampling, the complex coupling effects between range and azimuth will severely degrade the target parameter estimation and coherent integration performance. To deal with this issue, a fast coherent integration detection method with random azimuth sampling is proposed, where range migration is firstly compensated by applying the range-frequency reversal transform. Then, the random phase fluctuation caused by the staggered PRI can be efficiently removed by applying the non-uniform FFT technique. Finally, a moving target can be well focused. Simulated results are provided to validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Pulse-agile radar systems are becoming more prevalent as the demand for adaptive and cognitive systems increases. This focus is motivated by the need for interference avoidance and spectrum sharing. Pulse agility within a coherent processing interval (CPI) or intra-CPI adaption has been shown to cause distortion, which will negatively impact the radar’s performance. This problem can be framed in the context of image processing such that an ideal range–Doppler image is corrupted by some point spread function. Deconvolution is then applied to remove this distortion and improve radar performance while maintaining the ability to use computationally efficient fast Fourier transform-based processing. [ABSTRACT FROM AUTHOR]

When driving on an iron-bridge, stationary iron-clutters cause disturbances in the detection of a moving target in an automotive radar system. In this Letter, the authors propose a moving target detection method that utilises phase similarity of the spatial domain on an iron-bridge. To analyse the spatial domain via the array antenna signal of the up- and down-chirp beat-frequencies, the frequency-modulated continuous wave (FMCW)-phased array radar signal was used. It is possible to match the up- and down-chirp beat- frequencies of each object, moving target, and stationary iron-clutters, by using the proposed method. Not only the moving target but also the ego-vehicle and moving target velocity are detected through this matching. The suitability of the proposed method is verified by on-road measurement data using a 77 GHz FMCW-phased array radar. [ABSTRACT FROM AUTHOR]

Multiple-input multiple-output (MIMO) radar has many advantages over the phased-array radar due to the waveform diversity, one of which is the greater flexibility to design the transmit beampattern. In this Letter, a low-complexity transmit beampattern design method, considering constant envelope (CE) waveforms, is proposed for the uniform linear array MIMO radar. First, the authors parameterise the waveform covariance matrix as the integral form of continuous spatial variable, by exploiting the beamforming weight vector in the main lobe region, to derive the closed-form solution of the waveform covariance matrix that fulfils positive semi-definiteness and uniform elemental power constraints. The transmit beampattern designed by the proposed method has the spatial characteristics of low main lobe fluctuation and peak-to-sidelobe level, and further mathematical explanation is illuminated. Next, they directly use the parameterised expression of waveform covariance matrix, approximately transformed into a discrete form of the spatial variable based on the Riemann integral definition, to efficiently synthesise correlated CE waveforms. The proposed method can provide transmit beampattern performance comparable to existing methods with a lower computational cost and ensure the CE property of the waveforms. The performance of the proposed method is verified and analysed via numerical examples. [ABSTRACT FROM AUTHOR]

The use of through-wall radar imagery for remote intelligence of building interiors is promising but challenging. Relevant information about human targets and room layout features is typically buried in clutter. In this Letter, the authors propose a methodology for automated extraction of information about stationary human targets behind walls. Based on treatment of the individual blobs found in the imagery, the method consists of thresholding, segmentation, classification and 3D visualisation. Although further optimisation of each of the steps is required, they demonstrate with two examples, including one cluttered scene, that the combination of these steps is effective at eliminating large amounts of clutter and identifying human targets behind walls. [ABSTRACT FROM AUTHOR]

In this Letter, the problem of waveform design for MIMO radar with good transmit beampattern performance is investigated. The binary transmit waveforms are designed via minimising the beampattern integrated sidelobe to mainlobe ratio. Since the resulting binary combination optimisation problem is NP-hard, a generalised likelihood ascent search algorithm is proposed to deal with it. Besides, the effectiveness of the proposed algorithm is demonstrated via simulation results. [ABSTRACT FROM AUTHOR]

For the synthesised aperture radar, the radar signal with a zero autocorrelation zone (ZACZ) is synthesised, which represents a sequence from two phase-code shift keying (PCSK) pulses coded by adjacent pairs of the D-code with additional linear frequency shift-keying (LFSK) of the train pulse discrete value. A comparative analysis is performed of correlation characteristics of the synthesised signal with the signal without discrete modulation and the truncated M-sequence. Total correlation characteristics of the ensemble from four signals are also analysed. It is shown that in ZACZ, the level of all side lobes of the autocorrelation function (ACF) of the synthesised signal is less than the level of the ACF side lobes of the M-sequence. The total ACF of the ensemble of four signals both with modulation and without the discrete modulation has zero side lobes along with the whole time axis t, and at mismatch in frequency in ZACZ, it has the side lobe level <-40 dB. [ABSTRACT FROM AUTHOR]

Although traditionally associated with defence and security domains, radar sensing has attracted significant interest in recent years in healthcare applications. These include the monitoring of vital signs such as respiration, heartbeat, and blood pressure, analysis of gait and mobility levels, classification of human activities to promptly detect critical events such as falls, as well as the evaluation of fitness and reactivity levels. The attractiveness of radar against alternative technologies such as wearable sensors or cameras lies in its contactless capabilities, whereby people do not need to wear, carry, or interact with any additional device, and plain images of people and private environments are not recorded. In this letter, we discuss some of the most recent achievements and outstanding research challenges related to radar applications in healthcare and present some results from our work at the University of Glasgow, including a dataset of radar signatures of human activities that are openly shared with the wider community. [ABSTRACT FROM AUTHOR]

When multiple ground-based differential interferometric radar (GB-DInRad) systems are utilised together to resolve threedimensional (3D) deformation, the resolving accuracy is related with the measurement geometry of these radar systems. This Letter focuses on how to determine an optimal geometry. Based on the resolving equation of the 3D deformation, the Geometric Dilution of Precision (GDOP) is defined. Then the minimum value of the GDOP is calculated and a detailed geometrical analysis is made to determine the geometrical conditions of the minimum GDOP. The results prove that the optimal geometry could be obtained when the unit measurement vectors of these radar systems construct a regular pyramid with a specific structure. A numerical simulation is utilised to validate the analysis conclusion. [ABSTRACT FROM AUTHOR]