Quanhua Liu

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.

Fresnel based frequency domain adaptive beamforming for large aperture distributed array radar

Distributed array radar is a significant radar system, which can not only improve radar detection capability and measurement accuracy, but also suppress mainlobe interference effectively. However, due to its equivalent large aperture, the plane wave assumption fails. Whats worse, target signals arriving at each array may have the envelope migration problem, thus the traditional adaptive beamforming method becomes invalid. This paper proposes a Fresnel based frequency domain adaptive beamforming method for large aperture distributed array radar. Instead of plane wave model, it uses the Fresnel model based steering vector to improve accuracy. Meanwhile, it transforms the time domain signal to frequency domain, and using the traditional adaptive beamforming method for each frequency point respectively. Finally, it accomplishes the frequency domain adaptive beamforming by an inverse Fourier transform (IFFT). In result, this method could eliminate the envelope migration problem effectively. Simulations illustrate the effectiveness of the proposed method.

Whitening filter for mainlobe interference suppression in distributed array radar

This paper proposes a mainlobe interference suppression method based on whitening filter for distributed array radar (DAR). Due to the equivalent large aperture of DAR, it is possible to cancel the mainlobe interference without target signal suppression. For narrowband signal, the time domain whitening filter (TD-WF) is used. As for the wideband signal or large aperture DAR, the target signals arriving at each antenna may have the envelope migration problem, thus the frequency domain whitening filter (FD-WF) is utilized in order to avoid this problem. In addition, a mainlobe interference suppression experiment is carried out in the scenario involving an S-band experimental radar system and an S-band jammer. The measured data is processed employing the proposed method, and the result verifies the effectiveness of this algorithm.

Modified position correlation method for high resolution radar target detection

Parameterized detection methods for high resolution radar target have the mathematical models mismatch problem. On the other hand, most parameterized range extended target detection algorithms are relatively complex and need a large amount of calculation. Thus these methods cannot satisfy the real-time processing requirements in engineering. In order to overcome the disadvantage of mathematical model mismatch and improve processing efficiency, this paper proposes a novel non-parametric double threshold detection method based on modified strong scattering point position information correlation. Measured data test shows that the algorithm can effectively detect the target and reduce the computational complexity.

Research on parameters estimation and suppression for C&I jamming

Chopping and Interleaving (C&I) jamming is a new technology to counter pulse compression radar. It can obtain partial processing gain and produce multiple false peaks, hence achieve both deception and suppression jamming effects. In this paper, the parameter estimation and suppression methods for C&I jamming are studied. With the derivation of the pulse compression result of the jamming, time-frequency analysis is applied for jamming parameter estimation; and then the jamming is reconstructed and cancelled. Because of the low estimation accuracy of the jamming time width, an adaptive CLEAN algorithm was proposed to improve the suppression performance. The effectiveness of the method is verified with simulation.

Target Tracking Using SePDAF under Ambiguous Angles for Distributed Array Radar

Distributed array radar can improve radar detection capability and measurement accuracy. However, it will suffer cyclic ambiguity in its angle estimates according to the spatial Nyquist sampling theorem since the large sparse array is undersampling. Consequently, the state estimation accuracy and track validity probability degrades when the ambiguous angles are directly used for target tracking. This paper proposes a second probability data association filter (SePDAF)-based tracking method for distributed array radar. Firstly, the target motion model and radar measurement model is built. Secondly, the fusion result of each radar’s estimation is employed to the extended Kalman filter (EKF) to finish the first filtering. Thirdly, taking this result as prior knowledge, and associating with the array-processed ambiguous angles, the SePDAF is applied to accomplish the second filtering, and then achieving a high accuracy and stable trajectory with relatively low computational complexity. Moreover, the azimuth filtering accuracy will be promoted dramatically and the position filtering accuracy will also improve. Finally, simulations illustrate the effectiveness of the proposed method.

Design and implementation of HPRF stepped frequency radar echo simulator

A HPRF stepped frequency radar echo simulator for performance evaluation and test of radar system is introduced in this paper. The echo model of HPRF stepped frequency radar is analyzed, and its expression, considering range ambiguity and relation between intermediate frequency bandwidth and range window, is given. This paper proposed an implement scheme of HPRF stepped frequency radar echo simulator based on DAC chip AD9736. The simulator can generate kinds of radar baseband and intermediate frequency waveforms realtime, including clutters and noise if needed. It also supports data replay and provides common digital interface such as Ethernet, RS422 etc. So the simulator has the feature of universal usage. Finally, testing result demonstrates the effectiveness of the simulator.