Guo-Sui Liu

Application of the fractional Fourier transform to moving target detection in airborne SAR

As a useful signal processing technique, the fractional Fourier transform (FrFT) is largely unknown to the radar signal processing community. In this correspondence, the FrFT is applied to airborne synthetic aperture radar (SAR) slow-moving target detection. For airborne SAR, the echo from a ground moving target can be regarded approximately as a chirp signal, and the FrFT is a way to concentrate the energy of a chirp signal. Therefore, the FrFT presents a potentially effective technique for ground moving target detection in airborne SAR. Compared with the common Wigner-Ville distribution (WVD) algorithm, the FrFT is a linear operator, and will not be influenced by cross-terms even if multiple moving targets exist. Moreover, to solve the problem whereby weak targets are shadowed by the sidelobes of strong ones, a new implementation of the CLEAN technique is proposed based on filtering in the fractional Fourier domain. In this way strong moving targets and weak ones can be detected iteratively. This combined method is demonstrated by using raw clutter data combined with simulated moving targets.

Random signal radar - a winner in both the military and civilian operating environments

Besides some general requirements, modern military radars should possess excellent LPI (low probability of intercept) properties. And civilian radars should satisfy the rigorous requirement of EMC (electro-magnetic compatibility) performance. The special features of random signal radar are analyzed here based on the different requirements for military and civilian use. Results show that random signal radar has excellent LPI property and EMC performance simultaneously, which can satisfy both military and civilian requirements.

The analysis and design of modern Low Probability of Intercept radar

In the modern battlefield, radar faces more and more serious threats from ECM and ARM, etc. Only the Low Probability of Intercept (LPI) radar can survive. In this paper, the principle of LPI radar is introduced first. Then the effects of radar parameters on LPI performance are discussed in detail. Finally, some advice is proposed for the design of the ideal LPI radar system.

Ship detection with short coherent integration time in over-the-horizon radar

To realize the ship detection with short coherent integration time (CIT) is an operational requirement for skywave over-the-horizon radar (OTHR). However, short CIT and the resulting low Doppler resolution cannot separate the ship from the close powerful ocean clutter. To resolve this problem, Fourier transform based clutter cancellation is proposed as well as some super-resolution spectral estimation techniques. In this paper, we still use a clutter subtraction scheme but the clutter parameter estimation is improved by analyzing the Fourier phase information. As a result, the estimation accuracy is enhanced and better cancellation performance may be achieved, which to some extent will decrease the power and spreading of clutter residue and benefit the ship visibility and identification.

The study on Doppler centroid estimation in DBS imaging

Doppler centroid estimation is one of the most important steps in Doppler beam sharpen (DBS) imaging of airborne pulse Doppler radar. Two improved Doppler centroid estimation techniques are proposed. They are called the weighted pattern match technique (WPMT) and curve fitting iterative technique (CFIT) respectively. These new algorithms avoid the effects of non-homogeneous scene and random fluctuation of echoes. The precision of the estimation is improved significantly. The processing results of raw radar data prove their effectivity.

A performance analysis of the MUSIC algorithm in the presence of amplitude and phase errors

This paper presents an analysis of the effects of amplitude and phase perturbation on the spectrum of the MUSIC algorithm. Theoretical expressions of the mean and variance of the spatial spectrum are derived, that is, we quantify the sensitivity of the MUSIC algorithm by first- and second-order statistical analysis. The expression reveals the relationship between the error of spectrum and the variance of the perturbation. The performance prediction is validated by computer simulation. The amplitude and phase perturbation decrease the peak values of the spectrum obviously and lower the resolving power, and the amplitude perturbation can result in spectrum error greater than that of phase perturbation for the case of the same variance of modeling errors.

The changeable sampling-rate processing technology with application to SAR-MTD

The echo of a moving target for airborne Synthetic Aperture Radar (SAR) can be approximated by the chirp signal. The changeable sampling-rate processing technology (CSPT) proposed by us is an effective technique to detect the frequency modulation rate of a chirp signal, but the remaining Doppler frequency diminishes its performance. In this paper, the influence of remaining Doppler frequency on the performance of CSPT is analysed and a new algorithm proposed to eliminate the remaining Doppler frequencies of all chirp components simultaneously based on the signal reconstruction from its ambiguity function. Therefore the improved CSPT can achieve excellent detection performance for the chirp signal. This method is applied to airborne SAR moving target detection (MTD), and the detection scheme is presented. Finally, the improved CSPT is demonstrated by using raw ground clutter data combined with a simulated moving target.

Signal processing of sky wave over-the-horizon radar

In this paper, A review of signal processing for sky wave over-the-horizon radar (OTHR) is presented. The radars operating mode, and its advantages and limitations are introduced firstly. Then the techniques on interference suppression, correction of some ionospheric contamination, and ship detection are reviewed in detail. At the end of this paper, the ways ahead in OTHR signal processing are also considered.

The Matched Transform based on Phase Compensation

In this paper, a new algorithm called Matched Transform based on Phase Compensation (MTPC) is proposed. By constructing the matched function, this algorithm can make the signal energy concentrate in the transform domain. And as the result, the good performance of signal detection and parameter estimation can be obtained. For continuous and discrete MTPC, the general form is firstly given, and then the MTPC of chirp signal is analyzed. In addition, the MTPC combined with Genetic Algorithm (GA) is also studied in this paper to detect and estimate the multi-parameter complex signal. The simulation results prove the validity of the algorithm.This paper addresses the problem of frequency overlapping which occurs when spectral estimation is applied after subband decomposition. Subband decomposition has already been shown to increase the performances of spectral estimation but induced frequency overlapping may be troublesome. This paper proposes a new spectral estimation procedure based on sub band decomposition and frequency warping which reduces the overlapping frequency problem. Simulations confirm the interest of this new algorithm.

Performance analysis of MVDR algorithm in the presence of amplitude and phase errors

The sensitivity of a spectrum estimation approach, the minimum variance distortionless response spectrum estimator, to random perturbations in the amplitude and phase of array sensors and channels is studied. Analytical expressions for the mean and variance of the spatial spectrum are derived. The effects of the amplitude error on the spectrum is greater relatively than that of the phase error. Theoretical results are validated by computer simulation. These expressions are then used to study the characteristics of the estimator.