Ning Tai

Joint estimation of DOA and mutual coupling via block sparse Bayesian learning

The direction-of-arrival (DOA) estimation accuracy is sensitive to the unknown mutual coupling in antenna array. This paper proposes an online array calibration method which jointly estimates the DOAs and the mutual coupling. Taking advantage of the Toeplitz property of mutual coupling matrix (MCM) with the uniform linear array (ULA), we handle the joint estimation problem by exploiting the block sparse Bayesian learning (BSBL) framework. This method does not need the calibrating sources or the preliminary MCM. Due to the robustness of the BSBL, this method is also effective under coherent scenario. The performance of the proposed method is compared with other well-known calibration algorithms and the Cramer-Rao lower bound (CRLB). The results show that it achieves higher accuracy and resolution.

Statistical Analysis of High-Resolution Coherent Monopulse Radar Sea Clutter

A statistical analysis that properly characterizes sea clutter processes is indispensable both for optimum detection algorithm design and for performance prediction problems in maritime surveillance applications. In this paper, we present the statistical analysis of experimental sea clutter data collected by a high-resolution coherent monopulse radar. First, we present the amplitude statistical analyses for these clutter data. The results show that the , Pareto, and CIG distributions can each provide good fits to the clutter data for three channels of monopulse radar. The analyses on the variations of the distribution parameters with range suggest that the scale parameter is closely associated with the clutter powers and that the shape parameter is influenced by the sea state. Then, we focus on the correlation properties. The averaged results suggest that the temporal and spatial correlation properties are similar for the clutter of all three channels. Moreover, the clutter between the sum and difference channels is almost completely correlated in elevation and is lowly correlated in azimuth. Finally, we perform a spectral analysis, highlighting the temporal and spatial variabilities of Doppler spectra. It is found that the individual Doppler spectra in all three channels can be represented by Gaussian-shaped power spectral densities, and their centroid and width can be modeled as two separate stage linear functions of spectrum intensity.

2-D off-grid DOA estimation using sparse Bayesian learning with L-shape array

To further improve the performance of the two-dimensional (2-D) direction-of-arrival (DOA) estimation, we propose a novel method employing the sparse Bayesian learning (SBL). In this new method the 2-D DOA estimation is divided into two independent 1-D DOA estimations which can be resolved by the SBL respectively. To avoid the negative effects on the accuracy of DOA estimation and signal reconstruction caused by grid mismatch in sparse reconstruction, the off-grid model is adopted. By exploiting the self-coherent property of signals, pair matching of elevations and azimuths is accomplished by pair matching of the two sets of reconstructed signals. Numerical simulation results demonstrate the superior performance of the proposed method.

Coherent noise jamming to de-chirping radar

Repeater jamming has become an important jamming type for countering coherent radar since it is proposed. In this paper, a coherent noise jamming method based on interrupted-sampling and pseudo-random sequence phase-modulation is proposed against de-chirping radar. The characteristic of jamming signal is analyzed in detail and the processing procedure of de-chirping radar is introduced. After De-chirping, multiple dense false-targets are formed to protect the true target. Compared with non-coherent noise jamming, this jamming signal is of much correlation with radar signal and capable of obtaining processing gain. At last, some simulation results are presented to validate the correctness and effectiveness of the jamming method. With the ability of adapting to different radar signals and the simple structure to be realized, this jamming idea shows some significance to engineering implementation of jammer.

Effects of Compound -Distributed Sea Clutter on Angle Measurement of Wideband Monopulse Radar

The effects of compound K-distributed sea clutter on angle measurement of wideband monopulse radar are investigated in this paper. We apply the conditional probability density function (pdf) of monopulse ratio (MR) error to analyze these effects. Based on the angle measurement procedure of the wideband monopulse radar, this conditional pdf is first deduced in detail for the case of compound -distributed sea clutter plus noise. Herein, the spatial correlation of the texture components for each channel clutter and the correlation of the texture components between the sum and difference channel clutters are considered, and two extreme situations for each of them are tackled. Referring to the measured sea clutter data, angle measurement performances in various K-distributed sea clutter plus noise circumstances are simulated, and the effects of compound K-distributed sea clutter on angle measurement are discussed.

A design of coherent moving target simulator for inverse synthetic aperture radar

The moving target simulator is an important but intractable issue in the performance evaluation of modern radar. The consistence and correctness of output target echo-wave must be considered and quantization error must be minimized to make the simulated waveform more like a realistic echo. However, most of the simulators are based on analog method and have limited capability of imitating complex target echo. When the properties of the simulated targets change, these simulators always need to alter the physical structure, which is of course not convenient. In this article, a moving target echo simulator for inverse synthetic aperture radar (ISAR) is introduced. This simulator is capable of producing target echo with minimized phase error. The phase error eliminating method in frequency domain is introduced in detail. Theoretical analysis and simulation results indicate that the proposed simulator can produce vivid moving target echo. The correctness of the method is further validated by the circuit implementation.

Multiple false targets jamming method based on FIFO

Efficient active jamming method against modern high resolution radars has been an important research topic in recent decades. The proposed researches introduce many methods to produce false targets jamming or noise depressing jamming. But many of them are somewhat complicated, with too much computing resources, and not possible to be implemented. This paper proposes a practical implementation method of multiple false targets jamming method based on FPGA, high speed AD converter and DA converter. According to the theory of matched filter in linear frequency modulated (LFM) radar, the delayed radar signal will result in a false target. Inspired by this property, we propose an active jamming method capable of generating multiple false targets based on first-in first-out (FIFO) in FPGA. The digital signal processing procedures in FPGA and the considerations on overflow of the superposition of multiple false targets are elaborately introduced. At last the FPGA implementation of the proposed method is introduced in detail and simulation results validate the effectiveness and correctness of our work.

The design of a novel coherent noise jammer against LFM radar

In this paper, a novel coherent noise jammer is proposed against the pulse compression radar. The algorithm is implemented by modulating the sampled radar signal according to the pseudo-random sequence. A high speed ADC is adopted to sample the baseband radar signal from 50MHz to 1150MHz and the parallel data processing in FPGA of Virtex-6 is introduced. The characteristic of the jamming signal in time domain and frequency domain is analyzed in detail. Mathematic expressions indicate that multiple false targets are induced after pulse compression and the real target is protected effectively. Compared with the traditional non-coherent noise jammer, the jamming signal created by our jammer is coherent with the matched filter and is able to obtain some processing gain. Simulation results and the implementation of the proposed method validate the correctness and effectiveness of the design.

Study on inverse synthetic aperture radar jamming method based on sinusoidal phase modulation

This paper focuses on the research of inverse synthetic aperture radar (ISAR) jamming method based on sinusoidal phase modulation. This method is used to intercept the enemys echo multiply the sinusoidal template for phase modulation, then send the result out. Imaging results in the ISAR system could get suppressed jamming result or multi false target jamming result. After the sinusoidal phase modulation jamming principle are expounded, the simulation result shows the validity and feasibility of this method. The relationship between amplitude and frequency control parameters with the jamming effect are deduced in theory. In simulation experiment, the relationship between the regulation of jamming signal periodic delay time and the jamming effect which is expounded, the same jamming result can be get by changing the signal periodic delay time without considering the factor of power and bandwidth. Because this method only needs a small amount of computation, it has a good guiding significance for the development and application of airborne or bomb jammer.

Novel noise jamming for countering ISAR based on pseudo-random serials phase-modulation

Scatter-wave jamming (SWJ) can form false target to inverse synthetic aperture radar (ISAR), while pseudorandom serials phase-modulation can spread the spectrum of target signal. Thus in this paper we propose an active quasi-coherent noise jamming signal by combination of these two methods. The jammer firstly intercepts the radar signal and then transmits the modulated jamming signal to protected target. It is demonstrated that noise image will be induced after target scatters the jamming signal back to ISAR. This jamming signal can form multiple noise-like false-targets in range direction. Simulation results validate the correctness of the idea and show that the jamming signal can effectively cover the true target.