Shunsheng Zhang

An advanced equivalent slant range model and image formation in geosynchronous SAR

Synthetic aperture radar on geosynchronous satellite (GEO SAR) has significant potential advantages over conventional low Earth orbit radars, albeit it also has challenges to overcome. In GEO SAR, the imaging geometry is more complicated and the range and azimuth variances are more severe. In order to deal with these problems, this paper presents an advanced equivalent slant range (AESR) model for the synthetic aperture radar undergoing an inclined circular orbit. Furthermore, the range and phase error between AESR model and conventional slant range model are also gauged in detail. Meanwhile, based on the AESR model, the accurate two dimensional (2-D) frequency spectrum (PTFS) expression of point target is obtained. And the modified algorithm and simulation results validate the AESR and show its advantages in image formation in GEO SAR cases.

Bistatic forward-looking SAR imaging based on two-dimensional principle of stationary phase

Synthetic aperture radar (SAR) techniques are typically used to achieve a high azimuth resolution, but conventional monostatic SAR is not applicable in forward direction because of azimuth ambiguities and poor Doppler resolution. In this paper, we present a new bistatic forward-looking SAR imaging algorithm based on point target reference spectrum using the two-dimensional (2-D) principle of stationary phase to improve the Doppler resolution and to avoid azimuth ambiguities. Based on the bistatic configuration and the novel algorithm, SAR not only can image the forward-looking terrain of the aerocraft, but also plays sufficient role in selflanding and navigation. Finally, simulations are used to validate the proposed spectrum and processing algorithm.

Flocking algorithms for multi-agent systems with time-delay

Focusing on the time-delay problem of multi-agent systems, this paper provides solutions for flocking of systems with time-delay. For the circumstance with a virtual leader, the agents would follow the virtual leader and achieve the same velocity asymptotically. Systems with homogeneous and inhomogeneous time-delays are discussed respectively. The appropriate simulation circumstance is set up, and the obtained results are in agreement with the theoretical deduction, which show the effectiveness of the proposed flocking algorithm.

A new method of phase compensating for moving targets in ISAR imaging

The traditional phase compensation method based on parametric model always needs to make a tradeoff between the accuracy and the computational complexity. Given this, a new method for compensating phase based on Discrete Polynomial Transform (DPT) and CLEAN technique is proposed. To reduce the computation power further, the imaging region estimation is applied. Furthermore, the limitation and the restricted condition of DPT are analyzed for practical scenarios in this paper. In the end, simulation results are given to validate this method.

Impact of antenna directing jitter in bistatic SAR

Bistatic synthetic aperture radar (SAR) system separated its transmitter and receiver, the spatial separation mode provides many technical challenges. This paper addersses on the issue of antenna directing jitter error, the impact of antenna directing jitter including fast jitter and slow jitter are analyzed respectively. In the case of fast jitter, a generalized mathematic model is employed to analyze the impact of antenna directing error on the echo signal, and concluded that the antenna shaking may produce paired echo, the position and the amplitude of the paired echo are analyzed, in the other case, the modulating effect is ignored, and the illuminating region of antenna beam is mainly considered, the impact of echo signal partly misses is introduced. In the end, the simulation results are presented to verify the analyses.

Passive radar detection with DVB-T signals

Passive radar system exploits illuminators of opportunity (IOs), such as television and radio, to detect and track moving targets. In this paper, we propose a new passive radar detection scheme with DVB-T signals. A large time-bandwidth-product signal is first generated by using multiple channels DVB-T signals. Then, a Radon-Fourier transform (RFT) algorithm is applied to achieve long-time coherent integration. In doing so, the moving target can be detected in low signal-to-noise ratio (SNR) situation. Simulation results validate the effectiveness of the proposed scheme.

An integrity monitoring method of satellite clock bias using Shewhart Control Chart

The accuracy of navigation and positioning directly depends on satellite clock bias. Because of different abnormal models, predicting and integrity monitoring of satellite clock bias is a great challenge. This paper described the satellite clock bias model, analyzed the reasons of abnormal satellite clock bias, and established three satellite clock models. Then, this paper validated the accuracy of two prediction model. At last, this paper proposed an integrity monitoring method using Shewhart Control Chart. Based on IGS products, through simulation analysis, we found that this method can successfully detect abnormal clock bias, monitor integrity of clock bias and replace outliers.

Anti-jamming performance evaluation based on GPS software receiver

Many anti-jamming techniques have been proposed such as adaptive temporal filtering (ATF), spatial adaptive processing (SAP), space-time adaptive processing (STAP), power spectrum excision, and etc. The performance of each specific anti-jamming technique is often evaluated in terms of tracking thresholds not in terms of range or position error. And several techniques can be combined together to provide better anti-jamming performance. How to judge the anti-jamming performance of these algorithms has become a new problem. In order to solve this problem, the anti-jamming performance of SAP and STAP based on linear constraint minimum variance (LCMV) criterion will be evaluated and compared through many indicators in this paper. Simulation results show that STAP with L constraints brings more degrees of freedom to constrain the weight coefficients and thus improve C/N0, especially when many jammers impinge on the array.