Wideband Radar Signal Research Articles

Advanced Copula-based Methods for Nonparametric Detection and Characterization of Wideband Radar Signals

This paper introduces advanced copula-based methods for the nonparametric detection and characterization of wideband radar signals. The research focuses on developing signal detection algorithms that are invariant to changes in the probability density function of the sounding or reflected signals, employing multiscale analysis techniques and copula-based statistics. Two primary approaches are explored: multiscale analysis using wavelet transforms and rank-based signal detection with copula-based ambiguity functions. Simulation results confirm the effectiveness of the proposed approaches. The research demonstrates that integrating rank-based methods with copula-based statistics significantly improves the detection and analysis of wideband radar signals, particularly in complex scenarios where signals exhibit intricate dependency structures. This comprehensive detection framework is well-suited for handling high-dimensional radar signal data, enhancing accuracy and reliability under varied conditions. Future work will focus on optimizing copula selection and permutation strategies to further improve performance.

A Photonics-Assisted Wideband Radar Jamming Signal Generator With Flexible Tunability and Multidimensional Optimization

In this article, a wideband radar jamming signal generator with flexible tunability and multidimensional optimization is proposed based on a dual-polarization Mach–Zehnder modulator (DPol-MZM) cascaded with a phase modulator (PM). Interrupted-sampling jamming is achieved with a sampling frequency of 1 MHz and duty cycles of 50% and 25%. Cross-cosinusoidal phase-modulated jamming with frequencies of 2 and 4 MHz is also built. A compound jamming signal that combines interrupted-sampling jamming and cross-cosinusoidal phase-modulated jamming is generated. The jamming effectiveness of the above schemes is evaluated, and multiple false targets are obtained after cross correlation with the original radar signal. The number of generated false targets can reach 12. The jamming mechanism of the proposed scheme is discussed, and the jamming effectiveness in radar imaging is also analyzed. The proposed scheme has a stable, compact, and efficient structure and meets the requirements of the electronic warfare system, which will get potential applications in future electronic warfare systems.

Statistical Computation for Multipactors in Arbitrary Microwave Devices

Multipactors are avalanches of secondary electrons occurred in high-power vacuum microwave devices. Accurate prediction of their occurrences is challenging, especially for devices with complex geometric cavities under complex excitations. In this article, a generalized statistical theory is derived for predicting multipactors occurred in arbitrary metallic cavities under arbitrary excitations. Its computation burden is independent on the number of electrons, enabling investigations for dynamic evolutions of multipactors even in the presence of huge amount of avalanching electrons. Exampled with coaxial, rectangular, and ridged rectangular waveguides and excited with sinusoidal, multicarrier, and wideband radar signals, dynamic electron populations and breakdown levels were computed. While the obtained results agree well with previously reported experiments and particle-in-cell simulations, these results also explain three special phenomena occurred during multipactors, verifying the validity and accuracy of the proposed solution.

11‐GHz‐Bandwidth Photonic Radar using MHz Electronics

AbstractThe ever‐increasing demand for high resolution and real‐time recognition in radar applications has fuelled the development of electronic radars with increased bandwidth, high operation frequency, and fast processing capability. However, the generation and processing of wideband radar signals increase the hardware burden on complex and high‐speed electronics, limiting its capability for applications that demand high spatial resolutions. Progress is being made, photonics‐assisted radars offer higher frequencies but still heavily rely on costly and sophisticated high‐frequency electronic devices such as benchtop digital microwave waveform generators that fundamentally constrain the bandwidth and the practical utility. Here, for the first time, a photonics‐based radar with >11 GHz bandwidth (exceeding 20 GHz without RF antenna bandwidth limitation) driven and processed by simple MHz‐level‐electronics‐based acoustic‐optic modulation is demonstrated, which radically eliminates the requirement for ultra‐fast GHz‐speed electronics for wideband radar signal generation and processing. This wideband radar achieves centimeter‐level spatial resolution and a real‐time imaging rate of 200 frames s−1, allowing for high‐resolution detection of rapidly moving blades of an unmanned aerial vehicle. This radar provides an important technological basis for next‐generation broadband radars with greatly reduced system complexity essential to ubiquitous sensing applications such as autonomous driving, environmental surveillance, and vital sign detection.

Electromagnetic Signal Modulation by Chromatic Dispersion in Phase Gradient Metasurface

Chromatic dispersion in phase gradient metasurface and its impact on the scattered electromagnetic signals are studied in this paper. Due to its intrinsic material dispersion and special spatial arrangement of unit cells, phase gradient metasurface possesses large chromatic dispersion for the scattering waves, resulting in anomalous reflection and refraction phenomena. Moreover, from the perspective of signal domain, the scattered waves no longer carry the whole information of the incident wave especially for the wideband ones, because different frequencies are scattered in different directions due to the large chromatic dispersion. This progress is equivalent to a signal modulation in each scattering direction. Here we proposed a simple calculation method to achieve the direction-related spectral response characteristic for a given metasurface using 2D Fourier transform of the 2D phase pattern. Furthermore, a typical wideband radar signal was adopted to give a visualized display of the modulation effect. The simulated results showed that the scattered signals were greatly distorted, causing the correlation reduction and range deviation in radar detection. This work opens a new possibility for metasurface to manipulate the signal characteristic of electromagnetic waves and may prompt new applications in antennas, communication and radar systems.

Frequency Diversity Gain of a Wideband Radar Signal

Wideband radar has high-range directional resolution, which can effectively reduce the fluctuation of echo and improve the detection probability of a target under the same detection probability requirement. In this paper, a unified wideband radar χ2 distribution target model with more practical significance is innovatively established, on which the probability density function and detection probability function of Swerling 0, Swerling II and Swerling IV targets are analyzed, respectively. A generalized “frequency diversity gain” of wideband radar is proposed and defined based on the contradiction between suppression of fluctuation and accumulation loss, which represents the ratio of Signal-to-Noise Ratio (SNR) gain between broadband signal and reference bandwidth signal under the same condition (when the reference bandwidth is used, the radar target has only one range unit), and the mathematical relation equation of the target detection performance and signal bandwidth (equivalent to the number of distinguishable range elements of the target) is given. A Monte Carlo simulation experiment is designed. Based on the target model established in this paper, the optimal number of target range units corresponding to different detection probability requirements is obtained, which verifies the correctness of the concept proposed in this paper.

LoRadar: Enabling Concurrent Radar Sensing and LoRa Communication

Miniature radar has demonstrated its great potential in smart homes, such as understanding the wellness of the residents and providing ubiquitous interactions. While it has many promising applications, it also results in congested RF (radio frequency) environments as there is an unprecedented amount of traffic in a smart home. To ease the strain on the limited spectrum, we ask the question that, can we reuse the sensing signals for data communication? With such a capability, we can improve the spectrum utilization by sharing the spectrum between sensing and communication systems. However, radar signals are customized for the sensing purpose and are incompatible with legacy communication standards. To address this challenge, we have an observation that, non-linearity effect in RF circuits can convert wideband radar signals into a LoRa signal. Based on this observation, in this paper, we present LoRadar, which enables an FMCW (Frequency-Modulated Continuous Wave) radar to carry LoRa signals in sensing waves. We present both the downlink and uplink design, enabling a LoRadar device to communicate with LoRa nodes in a bi-directional way. We implement LoRadar and evaluation results show that LoRadar can achieve home-level coverage with 3.4kbps data rate while it preserves the sensing resolution of the radar.

An FPGA-based Direct Sampling and Digital Processing System for Wideband and Narrowband Radar Signal

This paper designs an integrated wideband and narrowband radar signal direct sampling and digital processing system based on FPGA. The system comprises a VPX case, a main board, a direct sampling board, a fiber board. It makes direct sampling of 1.8GHz-3.0GHz echo waves, with 3.2GHz sampling rate. The wideband and narrowband echo waves share the same ADC channel. After ADC sampling, both of wideband and narrowband data are exported to a mix-free digital quadrature demodulation module in FPGA. The narrowband data will be further processed by digital frequency down conversion. The wideband data will be further processed by digital de-chirp operation, with parallel DDS structure and multi-level decimation filters. Data rate of both the wideband and narrowband data after processing is decreased obviously. The designed sampling system cut down the analog radar signal processing operation, and decreases signal distortion. Besides, it integrated the reception, sampling and processing of wideband and narrowband signal, simplified the structure of radar system.

Deception Jamming Against ISAR Based on Convolution and Sub-Nyquist Sampling

This paper proposes a deception jamming method against inverse synthetic aperture radar on the basis of a simplified convolution method. Samples of a wideband radar signal are extracted using a sub-Nyquist sampling signal. A jamming signal is then generated by the parallel convolution of the extracted radar signal and high-resolution range profile of a target model. Introducing the sub-Nyquist sampling transforms the convolution into a parallel formation, which has a simpler structure and can be computed in real time. Furthermore, the computation complexity of convolution is reduced. The high-resolution range profile contains the scattering and movement properties of the target model, and the jamming signal is thus able to form vivid false targets on the ISAR image. Adjusting the frequency of sub-Nyquist sampling signal allows flexible control of the number and distribution of false targets. Simulation results are provided to verify the validity of the proposed jamming algorithm.

Extended Target Echo Detection Based on KLD and Wigner Matrices.

With the development of airborne radar radio frequency stealth (RFS) technology, the method of improving the RFS performance of airborne radar by optimizing target detection performance has been extensively studied. However, for wideband radar signals, the traditional point target model appears as an extended target model in the range-dimension, which is unfavorable to the detection of target echoes. To overcome the existing drawbacks, this paper devises an efficient echo detection algorithm from the perspective of information theory and random matrix. Firstly, aperiodic agile wideband radar signals are utilized to observe targets. Then, one frame of echo signals in the same range gate is reconstructed into a data form conforming to the Wigner matrix spectral decomposition. Finally, according to the signal detection theory, Kullback-Leibler Divergence (KLD) is used as the test statistic to complete the echo detection of the stealthy extended targets. By statistical analysis and comparison with other established echo detection algorithms, simulation results manifest that the proposed algorithm has superior detection performance and strong robustness, which not only makes up for the deficiency of traditional narrowband radar detection algorithms, but also increases the detection probability of radar system when it is faced with stealthy extended targets.

Extraction method of wide‐band phased array radar signals based on pulse amplitude characteristic

Wide-band phased array radar is the primary focus in electronic countermeasure reconnaissance, and prior extraction of such radar signals in the interleaved pulse data intercepted by the receiver has important military significance. Aiming at full pulse data intercepted by the receiver, a prior extraction method of wide-band phased array radar signals is proposed in this study. Utilising the electronic scanning feature of wide-band phased array radar, analyse the unchanging characteristic of pulse amplitude under the same working mode, and combine the pulse width characteristics of wideband pulse, a dichotomising reasoning algorithm in bioinformatics is introduced in this study. Firstly, reorder the full pulse data, filtrated by pulse width threshold, according to pulse amplitude; then, test the discontinuity points of pulse amplitude by employing the dichotomising reasoning algorithm, dividing the pulse sequences into segments with the same pulse amplitude; lastly, conduct pulse number threshold filtering on every segment, realising the extraction of wide-band phased array radar signals. The validity of this method has been verified by simulation experiments.

Method for compensating bandwidth error of synthetic wideband radar signal

The synthetic wideband signal has the advantages of high range and velocity resolution. It has a wide range of applications in target detection and recognition. While in the processing of signal generation, due to the improper setting of hardware system parameters, the bandwidth of the transmitting signal may not be consistent with the nominal value, which will affect the result of signal processing. In this study, the influence of system bandwidth error on synthetic high-resolution range profile is theoretically analysed. On this basis, an error compensation method based on parameter traversal is proposed and verified with simulation and experimental data processing.

Wideband Radar Signal Distribution With an Idler-Free Photonic Microwave Frequency Shifter

We demonstrate a novel scheme that combines photonic microwave frequency conversion and fiber transmission to achieve millimeter-wave (mm-wave) wideband radar signal generation and distribution for distributed radar systems. The principle is based on optical carrier-suppressed single-sideband modulation with an integrated polarization-division multiplexing dual-parallel Mach–Zehnder modulator. The idler frequencies in photonic microwave mixing are eliminated by controlling the modulator biases. And the fiber dispersion induced microwave power fading problem related with traditional double-sideband modulation is effectively avoided. The microwave phase distortions induced in the optical and electrical domains are investigated and compensated with electrical pre-distortion. Generation of an mm-wave wideband radar signal at a center frequency of 34.5 GHz with the bandwidth of 9 GHz and its transmission over a 40.8-km single-mode fiber with negligible degradation in pulse compression performance is achieved.

Design and Processing of a Novel Chaos-Based Stepped Frequency Synthesized Wideband Radar Signal.

The linear stepped frequency and linear frequency shift keying (FSK) signal has been widely used in radar systems. However, such linear modulation signals suffer from the range–Doppler coupling that degrades radar multi-target resolution. Moreover, the fixed frequency-hopping or frequency-coded sequence can be easily predicted by the interception receiver in the electronic countermeasures (ECM) environments, which limits radar anti-jamming performance. In addition, the single FSK modulation reduces the radar low probability of intercept (LPI) performance, for it cannot achieve a large time–bandwidth product. To solve such problems, we propose a novel chaos-based stepped frequency (CSF) synthesized wideband signal in this paper. The signal introduces chaotic frequency hopping between the coherent stepped frequency pulses, and adopts a chaotic frequency shift keying (CFSK) and phase shift keying (PSK) composited coded modulation in a subpulse, called CSF-CFSK/PSK. Correspondingly, the processing method for the signal has been proposed. According to our theoretical analyses and the simulations, the proposed signal and processing method achieve better multi-target resolution and LPI performance. Furthermore, flexible modulation is able to increase the robustness against identification of the interception receiver and improve the anti-jamming performance of the radar.

The GPU implementation of micro - Doppler period estimation

Aiming at the problem that the computational complexity and the deficiency of real-time of the wideband radar echo signal, a program is designed to improve the performance of real-time extraction of micro-motion feature in this paper based on the CPU-GPU heterogeneous parallel structure. Firstly, we discuss the principle of the micro-Doppler effect generated by the rolling of the scattering points on the orbiting satellite, analyses how to use Kalman filter to compensate the translational motion of tumbling satellite and how to use the joint time-frequency analysis and inverse Radon transform to extract the micro-motion features from the echo after compensation. Secondly, the advantages of GPU in terms of real-time processing and the working principle of CPU-GPU heterogeneous parallelism are analysed, and a program flow based on GPU to extract the micro-motion feature from the radar echo signal of rolling satellite is designed. At the end of the article the results of extraction are given to verify the correctness of the program and algorithm.

Progressive compressive sensing for exploiting frequency-diversity in GPR imaging

The microwave imaging of buried targets from wide-band ground penetrating radar (GPR) signals is addressed. By considering a contrast source inversion (CSI) formulation of the inverse scattering equations and taking advantage of both the intrinsic frequency diversity of GPR data and the sparseness of the unknown buried scatterers within the subsurface domain of investigation, a multi-task Bayesian compressive sensing (MT-BCS) approach is integrated within a frequency hopping (FH) inversion scheme. Towards this end, an innovative “constrained” relevance vector machine (C-RVM) solver is developed to effectively exploit the information, progressively acquired at each frequency step, on the unknown scattering scenario. Representative numerical benchmarks and preliminary experimental results are presented to assess the effectiveness and the potentialities of the proposed subsurface imaging method (namely, the FH-MT-BCS technique).

An Efficient Processing Architecture for Range Profiling Using Noise Radar Technology

The importance of high resolution range profiles (HRRPs) for radar applications like tracking or classification is well known. In the scientific literature several approaches have been investigated to obtain HRRPs from wideband radar signals. Recent works show that noise radar waveforms can be exploited in this sense due to their high resolution and low peak to sidelobe ratio (PSLR) properties. However their use can cause some issues in applications where long time integrations are required, e.g., in the presence of a low effective radiated power (ERP) transmitter: recording the reference signal in this case would be difficult due to the big quantity of data. This work proposes a real time digital processing schematic based on linear feedback shift registers (LFSRs) which is very flexible and has a low computational burden: its internal state can be easily controlled and reproduced in reception, where a multichannel correlator is exploited as matched filter. The resulting signal, compared to typical “pulse compression” and noise radar waveforms, shows similar performances but a lower order of complexity in terms of real time generation and reception.

Non‐uniform sampling and super‐resolution method to increase the accuracy of tank gauging radar

Different methods are proposed for fluid level measurement in storage tanks. Majority of these methods have some in-contact elements or are based on mechanical waves which are vulnerable to changes due to temperature change, pressure change or ageing. Electromagnetic based (i.e. radar) level measurement is a contactless method and it is less vulnerable to such changes. However, a wide band or ultra-wide band radar signal should be transmitted in order to achieve the required accuracy. Usually, linear frequency modulation or step frequency waveforms are used for this goal and matched filter (MF) processing or fast Fourier transform (FFT) are used to find the true level of the liquid inside the tank. In this study, the authors have shown that, those super-resolution methods used for array signal processing and direction finding can be also used in tank gauging problem. Through the simulations and also practical laboratory test, it is shown that, if the frequency steps are selected non-uniformly, the super-resolution methods produce more accurate result compared with MF or FFT processing.

Reconstruction of Wideband Radar Signal Based on Compressed Sensing

The matched filter is often used for the radar receiving terminal, but such application in wideband radar may cause complex system and high cost. The adoption of compressed sensing can not only remove the matched filter and the high-speed analogdigital converter, but also realize high-resolution radar imaging. In consideration of the sparseness of the radar target scene, a compressed sensing method used for chaotic radar is proposed in this article, wherein the chaotic frequency-modulated signal is generated by Bernoulli mapping and the randomness of such signal can be directly used for constructing the observation matrix. Meanwhile, the under-sampled echo signal can be used for radar scene reconstruction through the optimization technology. According to the simulation of stationary and non-stationary target radar scenes, compared with the matched filter processing technology, the proposed method has simple processing procedure and optimal performance, and the feasibility of this method is also verified by the simulation result.

Impact of wide-band I/Q modulation errors in SAR imaging analysis and compensation method resaerch

Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.