Xiaofeng Ai

Bistatic scattering centres of cone-shaped targets and target length estimation

The bistatic scattering centres are commonly modeled as the fixed scattering centres for imaging; however, the location of the bistatic scattering centre changes with the bistatic geometry in some real scenes. This paper focuses on the bistatic scattering centres of cone-shaped targets and considers how to utilize the length of the bistatic high-resolution range profile (HRRP) for target identification. Firstly, the locations of the bistatic scattering centres on the edge of a cone-shaped target are deduced with the method of equivalent currents, which are the intersection points of the edge and the plane constructed by the symmetry axis and the bisector of the bistatic angle. Then, based on the above conclusion, the wideband echo model and bistatic HRRP of a cone-shaped target is deduced. Then, the relation between the length of the bistatic HRRP and target length is deduced, which is useful for target identification. Finally, the bistatic HRRPs of cone-shaped targets are calculated via the Feko software and the calculated results validate the theoretical analysis. This research provides an exact mathematics model for the echo simulation, imaging, feature extraction and identification of cone-shaped targets in the bistatic radar.

Imaging of Spinning Targets via Narrow-Band T/R-R Bistatic Radars

The 2-D image of a spinning target obtained by monostatic radar is modified by the angle between the spinning axis and the radar line of sight, so it usually cannot describe the real size of the target. The T/R-R bistatic radar is proposed to solve this problem. First, the bistatic geometry and bistatic echo signals of a spinning target are modeled. Then, a novel 2-D imaging algorithm is presented based on the connections between the mono- and bistatic echoes of the same scatterer and the classical Hough transform, allowing both the mono- and bistatic 2-D images of the spinning target to be obtained simultaneously. The theoretical analysis is carried out by the electromagnetic calculation and numerical simulations.

An Equivalent Simulation Method for Pulse Radar Measurement in Anechoic Chamber

When a pulse radar signal is implemented in a range-limited anechoic chamber for radar measurement, the transmitted and reflected signal will be coupled at the receiver. To solve this problem and equivalently simulate the whole process of pulse radar measurement in an anechoic chamber, the interrupted transmitting and receiving method is proposed in this letter based on interrupted sampling. The constraints of the transmitting and receiving parameters are deduced with the sizes of the anechoic chamber and target. The pulse compression of the proposed method is performed. Then, the window function is applied to extract the main peaks after pulse compression. Both the simulation and experimental results are provided to demonstrate the effectiveness of the proposed method in overcoming the coupling between the transmitted and reflected pulse signals.

Bistatic two-dimensional imaging of spinning targets

The two-dimensional (2-D) image of a spinning target obtained by monostatic radar is modified by the angle between the spinning axis and the radar line of sight (LOS), so it usually cannot describe the real size of the target. The T/R-R bistatic radar is proposed to solve this problem. First, the bistatic geometry and bistatic echo signals of a spinning target are modeled. Then, a novel 2-D imaging algorithm is presented based on the connections between the mono- and bistatic echoes of the same scatterer and the classical Hough transform (HT), allowing both the monostatic and bistatic 2-D images that coincide with the real target to be obtained simultaneously. The theoretical analysis is validated by the simulation and electromagnetic calculation.

High resolution range profile reconstruction for rotating targets based on random stepped frequency signal

To extract the micro-motion parameters of the rotating targets, SFS (Stepped Frequency Signal) is usually adopted to obtain the HRRP (High Resolution Range Profile). To reduce the sub-frequency counts SFS needs to synthesize the wideband, RSFS (Random Stepped Frequency Signal) is raised. By randomly transmitting the sub-frequencies of SFS, the frequency counts are obviously reduced. Then HRRP reconstruction algorithms based on compressed sensing theory are proposed for the received sparse echo. Both math simulations and field experiments are conducted to prove the effectiveness of the proposed algorithm. The experiment results indicate that when the selected sub-frequency count of the RSFS is no less than some lower bounds, the recovered HRRP is qualified for the micro-motion parameter extraction of the rotating targets.

Extended target detection of MIMO radar based on GLRT in compound-Gaussian clutter

Multiple-input multiple-output (MIMO) radars with wideband signals are useful to discriminate target in clutter. With wideband MIMO radar, the problem of extended target detection in compound-Gaussian clutter is considered in this paper. By obtaining target echoes from each antenna, the detector based on generalized likelihood ratio test (GLRT) is developed. It shows that the shape parameter of clutter, Doppler mismatches and antenna configurations of MIMO radar heavily affect the performance of GLRT detector. Therefore, the detection performance is respectively analysed with different shape parameters and Doppler mismatches. By using maximum likelihood estimation (MLE), the detection curves with typical parameters are presented to illustrate that the proposed detector outperforms that obtained in Gaussian clutter. Then, the detection performance is discussed with different antenna configurations. Mathematical analysis and simulation results show that the detection performance reaches the best when the numbers of transmitters and receivers are equal, which provides reference for the antenna configuration of MIMO radar.

Data-driven method of reverse modelling for multi-function radar

The common researches for radar system modelling are mostly based on deductive methods, which forward simulate the radar working process according to the information of radar parameters and expert system. However, the radar prior information obtained is limited under battlefield background. So it is difficult to model the radar operating modes and schedule schemes accurately, especially for the multi-function radars (MFRs) which are able to employ multiple modes flexibly. A novel method of reverse modelling for MFR is proposed. The information of the waveform is translated into grammar according to the theory of formal language, and the corresponding Finite-state Automaton (FSA) is composed as initialization. Then, according to the thought of data-driven, the transition relations and probabilities between MFR modes are yielded by analysing the intercepted signals. Finally, the stochastic finite automaton (SFA) is composed, achieving the MFR model by reverse modelling. Simulation with hypothetical MFR signal data is presented, showing that the proposed method is able to compose its SFA effectively, which can be used in MFR state recognition to support the adaptive radar countermeasures.

A micro-motion information reconstruction method based on compressed sensing for precession ballistic targets

For a wideband radar system adopting stepped frequency signal (SFS), the micro-motion parameter is usually obtained by time-frequency analysis of the echo HRRPs (high resolution profiles). The data to be collected mainly includes each sub-frequency echo in the slow-time domain, which brings a great burden to the signal generation equipment and data storage on the radar system. Because of the sparseness of the ballistic target scatters in high frequency area, this paper adopts the compressed sensing technique to reduce the sampling data by randomly transmitting the stepped frequency signal. The performance of the proposed method is analyzed by the precession target measurement experiment in the anechoic chamber. The experimental results show that for the nose cone, middle circular ring and bottom circular ring of experimental missile target, when the sampling rate is no less than 50%, 30% and 30% respectively, the reconstruction result is qualified for micro-motion parameter extraction.

Full-polarization bistatic scattering characteristics analysis of stealth aircraft

Summary form only given. Bistatic radar is a hot research topic in recent years, especially about passive bistatic radar and bistatic SAR, however, the polarimetric bistatic scattering characteristics of the target is not researched enough, which limits the detection and recognition capability of the bistatic radar. The whole spatial polarimetric bistatic scattering data of the full-size stealth aircraft model are calculated with the multi-level fast multipole algorithm (MLFMA) via the electromagnetic calculation software. The fluctuation characteristic statistic of the polarimetric bistatic radar cross section (RCS) is carried out, and it is found that the statistical properties of the four kinds of polarimetric bistatic RCS are nearly the same, while the monostatic main and cross polarization RCS statistical properties are quite different from each other as shown in Fig. 1. It is also found that dynamic ranges of the four polarimetric types of bistatic RCS is larger than the monostatic case and the mean values of the four polarimetric types of bistatic RCS are larger than the monostatic case. The distribution characteristics statistic of the monostatic and bistatic polarization ratio is carried out and it is found that the monostatic and bistatic cross-main polarization ratios are quite different, while the main polarization ratios are similar. So any type of polarization is suitable for the bistatic radar while only the main polarization for monostatic radar. What is more, the full polarimetric capability is strongly recommended for bistatic radar. All the statistic results also provide a theory reference for fully polarimetric bistatic radar stealth aircraft target detection experiments.

Quantitative evaluation for self-screening jamming effectiveness based on the changing characteristics of intercepted radar signals

In the process of adaptive radar countermeasure, it is critical to evaluate the jamming effectiveness. Most of conventional methods rely on the data collected on radar side, which is unavailable under battlefield background. An approach for evaluating the effectiveness of self-screening jamming quantitatively from the view of reconnaissance and jamming systems is proposed. Since the amplitude and data rate of intercepted radar pulses before and after jamming vary obviously, the accumulated amplitude extracted from signals is chosen as the characteristic statistic. According to the response mechanism of jammed radar, the effectiveness evaluation detector is designed based on the theory of significance test. Under the condition of typical scenario in which ship-borne air-defense radar operates, simulations are performed to evaluate jamming effectiveness utilizing the proposed method. Simulations suggest that the results of evaluation appear completely consistent with the message displayed on radar side, which attests the validity of the approach.