Radar Signal Generation Research Articles

Photonics-based wideband multi-format tunable radar jamming signal generator

A photonics-based radar jamming signal generator is proposed in this paper. By adjusting a polarization controller, interrupted-sampling repeater jamming (ISRJ), comb spectrum modulation jamming (CSMJ), ISRJ and CSMJ composite jamming can be respectively generated after photoelectric conversion. We have experimentally verified the generation of ISRJ signals with duty cycles of 50% and 25%, the generation of CSMJ signals with comb spectrum frequency intervals of 5 MHz and 10 MHz, and the generation of their composite jamming signals in the Ku band. Additionally, the ISRJ and CSMJ composite jamming effect of radar signals in the Ka band has been tested. After matched filtering processing, multiple false targets are produced and the total number of jamming targets can be up to 25, demonstrating significant jamming effects. The proposed structure can generate multi-format jamming signals without using digital radio frequency memory, which is suitable for producing high-frequency and large-bandwidth jamming signals. It can be applied in electronic countermeasure systems.

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.

Tunable radar compound coherent jamming signal generation based on microwave photonics.

A photonic-assisted scheme to generate radar compound coherent jamming signals based on a dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed and experimentally demonstrated. The received linear frequency-modulated (LFM) signal is interrupted sampled and comb spectrum modulated by a DP-MZM. After photoelectric conversion, the compound coherent jamming signal, which combines the comb spectrum modulation jamming (CSMJ) and interrupted sampling repeater jamming (ISRJ), is generated. In the experiment, the generated coherent jamming signals have a 1-GHz bandwidth centered at 8 GHz and 18 GHz, respectively. The tunability of the frequency interval for CSMJ, the duty cycle, and the sampling frequency for ISRJ are verified. After pulse compression (PC), 10 false target groups are evenly distributed over a radial distance of 120 m, and the total number of false targets reaches to 50. The jamming effectiveness in radar imaging is also demonstrated. To the best of our knowledge, photonic-assisted CSMJ and ISRJ compound jamming generation is proposed for the first time. The proposed scheme is compact, wideband, and tunable, which shows a good potential application in the future electronic warfare system.

Small RCS targets detection based on pulse compression radar signal generator and processor

In the last two decades, field programmable gate arrays (FPGAs) have become the leading technology for implementing real time systems, specially radars. The most important advantage of FPGA is its parallel nature of executing complicated algorithms. As a result, the received data flow will be processed in a real time manner, which is suitable for radar applications. This paper attempts to show the design and the FPGA implementation of a binary phase-coded pulse compression radar signal generator and processor, that are intended to determine the ranges, and the speeds of targets with small radar cross-section area like drones. The system operating waveform is a bi-phase sequence, that is known to have the best known peak sidelobe level compared to compound Barker codes of the same length. In addition, the design incorporates a range sidelobes cancellation method to remove the time sidelobes in the matched filter output. Also, we are going to represent and investigate the FPGA implementing steps of the radar waveform generator and processor according to the required parameters. Finally, the implementation results of the proposed system will be represented.

Photonics-Based Radar Jamming Signal Generation and Self-Interference Cancellation

A radar jamming signal generation scheme based on microwave photonics is proposed. This model includes frequency shifting jamming signal generation and self-interference cancellation (SIC). In the scheme, the upper dual-drive Mach–Zehnder modulator (DDMZM) of a dual-parallel dual-drive Mach–Zehnder modulator (DP-DDMZM) is used to recover the signals-of-interest (SOI) by subtracting the self-interference signal from the received radar signal. The lower DDMZM of the DP-DDMZM is utilized to shift the frequency of the optical carrier by Serrodyne modulation. The output of the DP-DDMZM is sent to a photodetector to obtain the frequency shifting jamming signal. In the experiment, the generation of velocity deception jamming and range deception jamming signals is demonstrated. The spurious suppression ratio of the generated velocity deception jamming signals is investigated. The SIC performance of the scheme for signals with different frequencies and bandwidths is also analyzed. Both velocity deception jamming and range deception jamming can be flexibly implemented with variable parameters. Both radar jamming signal generation and self-interference cancellation can be implemented with only one DP-DDMZM, which has the advantages of a simple structure and easy integration.

Photonic-assisted generation of joint radar and communication signals with immunity to power fading

In this paper, a photonic-assisted generation of joint radar and communication signals with immunity to power fading is proposed based on a dual-polarization binary phase-shift keying (DP-BPSK) modulator. Two dual-drive Mach–Zehnder modulators (DD-MZMs) named DD-MZM1 and DD-MZM2 are respectively located on the upper and lower arms of the DP-BPSK modulator. In DD-MZM1, an intermediate frequency communication signal is single sideband (SSB) modulated on the optical carrier. At one radio frequency (RF) port of DD-MZM2, a split parabolic waveform signal is phase-modulated on the optical carrier to generate SSB radar signal, and the other RF port is used to phase modulate local oscillator signal. By simply adjusting a polarization controller, radar or communication signal can be respectively generated at different frequency band after balanced photoelectric conversion. Experiments are carried out to verify the feasibility of the scheme. Radar signals with bandwidths of 500 MHz and 1 GHz are generated. The error vector magnitude of the generated 16-QAM signal with a baud rate of 100 Msym/s is 5.42%. The frequency tunability and the immunity to power fading are also verified. The proposed method has a simple and compact structure and meets the requirement of long-distance transmission, which has potential applications in emerging intelligence scenarios.

Human Activity Classification Based on Dual Micro-Motion Signatures Using Interferometric Radar

Micro-Doppler signatures obtained from the Doppler radar are generally used for human activity classification. However, if the angle between the direction of motion and radar antenna broadside is greater than 60°, the micro-Doppler signatures generated by the radial motion of human body reduce significantly, thereby degrading the performance of the classification algorithm. For the accurate classification of different human activities irrespective of trajectory, we propose a new algorithm based on dual micro-motion signatures, namely, the micro-Doppler and interferometric micro-motion signatures, using an interferometric radar. First, the motion of different parts of the human body is simulated using motion capture (MOCAP) data, which is further utilized for radar echo signal generation. Second, time-varying Doppler and interferometric spectrograms obtained from time-frequency analysis of a single Doppler receiver and interferometric output data, respectively, are fed as input to the deep convolutional neural network (DCNN) for feature extraction and the training/testing process. The performance of the proposed algorithm is analyzed and compared with a micro-Doppler signatures-based classifier. Results show that a dual micro-motion-based DCNN classifier using an interferometric radar is capable of classifying different human activities with an accuracy level of 98%, where Doppler signatures diminish considerably, providing insufficient information for classification. Verification of the proposed classification algorithm based on dual micro-motion signatures is also performed using a real radar test dataset of different human walking patterns, and a classification accuracy level of approximately 90% is achieved.

Signal Calibration and Noise Reduction for Software-Defined Radio-Based GPR

This article studies signal calibration, frequency response estimation, and noise reduction for a software-defined radio (SDRadio)-based ground-penetrating radar (GPR). The radar signal generation utilizes the stepped frequency continuous wave (SFCW) method. The signal calibration takes advantage of the dual-channel structure of the SDRadio and solves the incoherent phase problem caused by phase mismatch between the local oscillators (LOs) in the transmitter and the receiver. The frequency response estimation involves two steps: First, the calibration measures the system’s intrinsic frequency response. Then it measures the frequency response of the target under the ground surface. The noise effect at the receiver is reduced using the ridge regression method. For performance evaluation, outdoor and indoor experiments are conducted, which show that the GPR A-scan waveform and B-scan image qualities can be effectively improved. Compared with the traditional method, the signal-to-clutter ratio (SCR) of the A-scan waveform is improved by around 7 dB and that of the B-scan image is improved by around 13 dB.

Detailed Analysis and Modeling of Phase Noise and Systematic Phase Distortions in FMCW Radar Systems

In coherent continuous-wave (CW) radar systems, such as frequency-modulated CW (FMCW) radar systems, measurement precision is distorted by phase noise and systematic phase errors during radar signal generation. Unfortunately, to date, these phase distortions have typically been modeled based on many simplifications, often leading to overoptimistic predictions of radar performance. For example, phase noise is regularly considered based on additive white Gaussian noise (AWGN) models, ignoring its colored spectral property. Systematic errors are also frequently not properly separated from stochastic distortions, or not precisely measured and modeled. To overcome these issues, an advanced CW radar and frequency synthesizer model is proposed, analyzed, and experimentally verified in this paper. It is shown how systematic phase errors can be measured and how the influence of phase distortions on radar measurement can be accurately predicted. The proposed modeling approach was investigated for range correlation and range precision. The key metrics are the phase noise power spectral density (PSD) for range correlation and the variance of the frequency estimate for range precision. A 24-GHz FMCW radar system was used for the experimental verification. Long-range radar targets with distances of 38 to 880 m were created with an analog fiber optical link. Therefore, a precise and systematic evaluation of all effects was possible. The proposed phase distortion modeling approach realistically represented the range-dependent radar measurement effects. This enables the most precise simulation of and prediction for FMCW radar performance to date.

Reconfigurable radar signal generator based on phase-quantized photonic digital-to-analog conversion.

A novel, to the best of our knowledge, scheme for reconfigurable radar signal generation is proposed based on the principle of photonic phase-quantized digital-to-analog conversion. Multi-level digital phase modulation with different modulation depths is combined to convert multi-channel digital data to the phase of an optical carrier. Frequency-modulated or phase-modulated radar signals are generated by beating the phase-synthesized optical carrier with a coherent reference light. The proposed radar signal generator features a simple structure, highly reconfigurable modulation format, and flexibly tunable frequency. A 3-bit photonic phase-quantized digital-to-analog converter with a 10-GSa/s sampling rate is constructed experimentally. The generation of linear frequency-modulated, nonlinear frequency-modulated, frequency-stepped, frequency-hopping, binary phase-coded, and polyphase-coded waveforms is demonstrated.

Feature Analysis and Extraction for Specific Emitter Identification Based on the Signal Generation Mechanisms of Radar Transmitters.

In this study, a feature analysis and extraction method was proposed for specific emitter identification based on the signal generation mechanisms of radar transmitters. The generation of radar signals by radar transmitters was analyzed theoretically and experimentally. In the analysis, the main source of unintentional modulation in radar signals was identified, and the frequency stabilization of the solid-state frequency source, the nonlinear characteristics of the radio frequency amplifier chain, and the envelope of the pulse front edge were extracted as features for specific emitter identification. Subsequently, these characteristics were verified through simulation. The results revealed that the features extracted by this method exhibit “fingerprint characteristics” and can be used to identify specific radar emitters.

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.

Pulsed-chaos MIMO radar based on a single flat-spectrum and Delta-like autocorrelation optical chaos source.

We propose and demonstrate a pulsed-chaos multiple-input-multiple-output (MIMO) radar system in this paper. In the proposed MIMO radar system, multi-channel pulsed chaotic signals are extracted from an optical seed chaos source with Delta-like autocorrelation and flat spectrum. The seed chaos source is generated by passing the chaotic output of an external-cavity semiconductor laser through a dispersive self-feedback phase-modulation loop and used for MIMO radar signal generation. The cross-correlation characteristics of MIMO radar signals, the maximum channel number of separable mixed echoes, as well as the performances of multi-target ranging and anti-interference in the proposed pulsed-chaos MIMO radar system are systematically investigated. The results indicate that multi-channel pulsed-chaos signals with Delta-like autocorrelation can be simultaneously generated from the seed chaos source, and excellent quasi-orthogonality of transmission radar signals can be guaranteed. Moreover, it is demonstrated that the proposed pulsed-chaos MIMO radar supports multi-target ranging with a centimeter-level resolution and can maintain satisfactory performance under low SNR scenarios with various interferences.

A Practical Deceptive Jamming Method Based on Vulnerable Location Awareness Adversarial Attack for Radar HRRP Target Recognition

In recent years, deep neural networks are increasingly popular in the field of radar high-resolution range profiles (HRRPs) target recognition. Unfortunately, recent researches have revealed that a deep-learning classifier can be easily fooled by adding small perturbations to the input, named adversarial attack. This provides us an inspiration for radar deceptive jamming signal generation in electronic countermeasures (ECMs). However, the perturbations generated by these adversarial attacks are usually of complex envelopes and quite low power, making it challenging for jammers to generate such actual jamming signals. To solve that issue, we propose a practical deceptive jamming generation method that learns the vulnerable range cells in an HRRP sample and injects several jamming pulses with specific amplitudes into these range cells. Such jamming signals are easy to generate and can deceive the radar automatic target recognition (RATR) model to output the wrong target category prediction with high confidence. To avoid the requirement of the recognition network structure information, we leverage the differential evolution optimization algorithm (non-gradientbased). Further, to provide the potential of real-time jamming signal generation during the test, an encoder is constructed not only to learn the separable features but also to find the vulnerable range cells and the specific amplitudes of the jamming pulses. In the experiments, we apply the proposed attack algorithms to fool the one-dimensional convolutional neural network-based HRRPRATR models. The extensive experimental results on measured aircraft HRRP dataset prove that the proposed algorithms achieve a promising attack performance and serve as a practical and fast deceptive jamming generation method.

Simulation and Synchronous Generation of Radar Signals at Geographically Distributed Sensors for Testing Emitter Location Systems

Location Fixing (LF) of Radar Emitters is carried out in an Electronic Warfare scenario by Sensors with Direction-of-Arrival and signal parameter measurement capabilities, geographically distributed over few tens of kilometres. The present paper brings out the Scenario Simulation and Synchronous generation of Radar Signal at Geographically distributed locations for comprehensive testing of the Emitter Location Systems (ELS). This test facility permits exhaustive testing of the ELS against various parameters since the performance of the ELS depends on factors such as Sensors’ geometry with respect to the location of the Emitter of interest, signal parameter measurement accuracies, LF algorithms used, time synchronization accuracy achievable among the Sensors, etc. The Radar signals are synthesized synchronously, locally, at each of the distributed Sensors by replicating the Emitter Signal characteristics as received at the Sensors. The Simulator System uses a High Accuracy GPS Receiver as the Global Clock against which the signals are timed and a Field Programmable Gate Array for generating controls triggered on the absolute time of the Global Clock.

Advanced Photonics-Based Radar Signal Generation Technology for Practical Radar Application

Photonics-based radar technologies can implement better performance in some main functionalities of the radar systems. The outstanding question is whether these technologies are suitable for the practical application of modern or future radars. Here, we comprehensively analyze key radar parameters and summarize the requirements for the practical applications. Then, we present the corresponding photonics-based technologies capable of meeting actual radar needs. From the aspect of radar signal requirements, we compare the typical microwave photonic technologies for the radar signal generation at this stage and guide the improvement direction. The paper reviews the photonics-based radar signal generation based on a phase-locked dual-comb in detail. Further, the innovative and scalable capabilities of the scheme are presented, including the multi-band radar signal generation for multiple functions radar, and high accuracy beamforming for advanced active phased array radar. The enhanced performances include more flexible carrier frequency, large modulation bandwidth, tunable pulse duration, configurable pulse repetition frequency, full coherence, and continuous phase shift with ultra-high accuracy. The proposed novel photonics-based technology will greatly push forward the application of microwave photonics technologies in actual radar systems.

Reconfigurable Photonic generation and transmission of multi-format radar signals

In this paper, photonic generation and transmission technique for multi-format microwave waveform is proposed. In the center office, a broadband optical source (BOS) is utilized as optical carrier. And the main component is a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM) followed by a polarization division multiplexed emulator (PDME). The DPol-DDMZM consists of two sub-DDMZMs to generate two orthogonally polarized optical signals. The system we proposed is conveniently reconfigured to generate different waveforms. By applying phase modulation (PM) to the orthogonal polarization states, a polyphase-coded microwave waveform with a tunable center frequency multiplication factor can be generated. By tuning the differential group delay (DGD) of the two polarizations by the PDME, the multiplication factor can be easily adjusted. In addition, if the carrier is suppressed at the upper and lower DDMZM, broadband dual-chirp microwave signal can be generated, transmitted over fiber and detected at a base station. The chromatic dispersion induced power fading is eliminated. The approach is investigated by simulations. Polyphase-coded signal with a repetition rate of 4 Gbit/s is demonstrated. And dual-chirp signal with a bandwidth of 8 GHz is carried out. Besides, the practical feasibility of the system is further studied by analyzing the power of the BOS, the relative time delay of PDME and the photonic integrated circuit (PIC) replica of the generator.

Broadband array radar based on microwave photonic frequency multiplication and de-chirp receiving (Invited)

Microwave photonic radar enables the generation and processing of broadband radar signals, which can significantly improve the range resolution of the radar system. To improve the radar angle resolution and realize flexible beam control, combining microwave photonic radar technology with array radar technology is an inevitable development trend. Previously, the optical truth delay technology is intensively investigated to achieve squint-free beam steering in broadband phased array radars, which usually face the problems of high complexity, poor flexibility, and limited delay accuracy. In recent years, the broadband radar architecture based on microwave photonic frequency multiplication and de-chirp receiving has received extensive attention. The array radar constructed based on this technology has wide operation bandwidth while enabling real-time digital compensation and processing functions, which provides a new idea for the development of broadband array radars. In this paper, the research progress of the broadband array radar based on microwave photonic frequency multiplication and de-chirp processing was reviewed. After expounding the transceiver mechanism of microwave photonic broadband radar, the method for constructing broadband phased array radar and the performance of digital beam scanning and imaging were introduced. Then, the radar array was extended to MIMO architecture. The broadband microwave photonic MIMO radar based on optical wavelength division multiplexing technology was introduced and its performance in target detection and imaging was analyzed.

Real-Time Signal Generator for Noise Radar

We present a real-time intermediate frequency noise radar signal generator that provides pseudo-random signals with uniform, normal, exponential, and Rayleigh probability distributions. In addition, normally distributed samples with uniform power spectral distribution with arbitrary bandwidths can be generated. The noise signal generator is implemented and tested on a Xilinx Ultrascale+ RFSoC FPGA based development board with the aim of testing the effect of distributions on target detection performance of the noise radar. The generator can also be used as a baseband signal source and an environment for noise radar waveform design.

Graphic User Interface Development of a Digital Phased Array Radar System

A graphical user interface (GUI) of a digital phased array radar system is developed to detect and reveal the supposed multi-targets. As the core of the digital radar system, the radar signal generation environment aims at producing a radar echo signal, which is achieved by superposing the simulated radar transmission signals, clutter, jamming signals and radar internal noise linearly; And the radar signal processing environment focuses on processing the radar echo signal to measure multi-target range and velocity information, by employing pulse compression (PC), moving target indication (MTI), moving target detection (MTD) and constant false alarm rate (CFAR) technologies. Every module of the core can be exhibited in the form of MATLAB GUI. In addition, an integrated GUI of the digital phased array radar system is constructed to offer all the multi-target detection and display functions.