Yongzhen Li

Micro-Doppler characteristics of sliding-type scattering center on rotationally symmetric target

The feature of micro-motion is one of the most effective features used for radar recognition in midcourse phase. At present, the study of feature extraction and recognition is usually based on the assumption that the micro-motion of the scattering center and warhead itself is the same, and the radar echo is sinusoid-FM signal. However, this assumption ignores the fact that the scattering center would slide on the warhead with the change of the aspect angle. In this paper, a complete micro-motion model is set for the scattering centers of different positions on the warhead, and the mathematical expression of the micro-Doppler of the sliding-type scattering center is obtained for the first time. The approximation of Taylor expansion under the background of missile confrontation is studied subsequently. The curve of this micro-Doppler is not the generally assumed sinusoid. Dynamic measurement of a precessional target in microwave anechoic chamber is done to vividly observe the sliding feature of the scattering center. The measurement results agree with the theoretic analysis in this paper. This research on micro-Doppler characteristics of sliding-type scattering center provides a more accurate model for the micro-motion simulation and feature extraction of precessional warheads.

A New Polarimetric Method by Using Spatial Polarization Characteristics of Scanning Antenna

Antenna polarization states always vary with scan direction. Here this phenomenon is called spatial polarization characteristic (SPC) of antenna. Based on the single polarized radar antenna, by sufficiently utilizing of the inherent polarization property of antenna (i.e. the property that polarization state is not a constant but a function of antennas spatial scanning direction), a novel polarization scattering matrix (PSM) measurement method is established. This method has the following advantages: (i) It does not need dual orthogonal polarization channels; (ii) the PSM of target can be obtained just by using the prior knowledge of SPC and by improving the signal processing mode of received radar signal. The modern radar systems can make use of this property in its measurement of target polarization scattering property in the searching or angle tracking stage.

Spatial polarization characteristics and scattering matrix measurement of orthogonal polarization binary array radar

Polarimetry is an important trend in the development of modern radar. The technique for measuring polarization scattering property of the target is the key for polarization radar realization, but it faces challenges in engineering. Here, a new theoretical model for target scattering characteristic measurement radar, named orthogonal polarization binary array radar (OPBAR), is proposed. The spatial polarization characteristics of the radar antennas are addressed. A new polarimetric algorithm that needs only one channel is designed. The polarization scattering matrix measurement can be implemented by processing received signal in a short time interval while antenna’s beam mechanically scans the target. Through compactness field microwave dark room experiment, measurments of dynamic broadband polarimetry on OPBAR have been conducted and the validity of research work has been demonstrated. The result is helpful to exploiting the capability of current radar systems and enhancing their information acquiring and processing capacity.

Instantaneous polarization statistics of electromagnetic waves

The problem of statistical description of instantaneous polarization of electromagnetic waves is studied. First, the physical meanings of instantaneous Stokes vectors’ components are analyzed, which provide a short cut for solving statistical distribution functions of instantaneous Stokes vectors. Second, in the condition of Gaussian hypothesis, the analytical expressions of probability density function (PDF) of instantaneous Stokes vectors are presented. Finally, some computation results are presented in the condition of two independent polarization channels, which show the validity and simplicity of the statistical description method.

The signal selection and processing method for polarization measurement radar

Based on the ambiguity function, a novel signal processing method for the polarization measurement radar is developed. One advantage of this method is that the two orthogonal polarized signals do not have to be perpendicular to each other, which is required by traditional methods. The error due to the correlation of the two transmitting signals in the traditional method, can be reduced by this new approach. A concept called ambiguity function matrix (AFM) is introduced based on this method. AFM is a promising tool for the signal selection and design in the polarization scattering matrix measurement. The waveforms of the polarimetric radar are categorized and analyzed based on AFM in this paper. The signal processing flow of this method is explained. And the polarization scattering matrix measurement performance is testified by simulation. Furthermore, this signal processing method can be used in the inter-pulse interval measurement technique as well as in the instantaneous measurement technique.

Improved Clutter Suppression Algorithm for Atmospheric Target Detection Using Polarimetric Doppler Radar

When using dual-orthogonal frequency modulation continuous wave (FMCW) polarimetric radar, the polarimetric range-Doppler spectra of the atmospheric targets are contaminated by noise, clutter, and artificial signals that disturb the analysis of atmospheric target parameters, such as reflectivity, mean Doppler velocity, and Doppler width. This paper describes an improved clutter suppression method that is able to detect most atmospheric targets while suppressing clutter, noise, and artificial signals as well as possible. By using logical decisions that are based on the spectral linear depolarization ratios (SLDRs), a binary mask matrix is constructed, and the characteristics of this original mask matrix are improved via mathematical morphology methods. To suppress clutter, noise, and artificial signals and retain atmospheric targets, we multiply the range-Doppler spectra by the improved mask matrix. The raw atmospheric data are acquired using the Polarimetric Agile Radar S- And X-band (PARSAX) radar, which is able to measure the backscattering matrix of atmospheric targets in one sweep. After calibration, the range-Doppler polarimetric spectra are processed using the proposed clutter suppression method, and the atmospheric targets are successfully detected. Compared with the unprocessed data and the data processed by noise clipping and double SLDR filtering, the data processed by the proposed method show improvement in the ability to determine the atmospheric targets in the range-Doppler spectrogram, the reflectivity, the mean Doppler velocity, and the Doppler width.

Statistical distribution of polarization ratio for radar sea clutter

Analyzing the statistical property of polarization ratio of radar sea clutter provides a reference for radar detection. In this paper, statistical distributions of the amplitude and phase of polarization ratio for radar sea clutter are analyzed. The sea clutter amplitude distributions in horizontal and vertical polarization channels are analyzed with real sea clutter data at first. Based on this, statistical distributions of the amplitude of the polarization ratio are derived. Analysis results of real sea clutter data are coincident with the theoretical derivation of the distribution of polarization ratio amplitude for sea clutter, and show that the distribution of polarization ratio phase approximates to Gaussian distribution.

Application of nonlinear polarization vector translation in radar anti-jamming

Nonlinear polarization vector translation (PVT) is applied in the area of radar anti-jamming in this paper. The processes of real number type and ratio type diagonal matrix PVT are analyzed, pointing out their deficiencies in polarization states separation of the target and jamming. Then exponential diagonal matrix PVT is proposed and show its advantage on both polarization state angle and polarization divergence. The result that Nonlinear PVT separates the target and the jamming on the Poincare sphere can help to improve the filter performance, bringing convenience to subsequent interference suppression, polarimetric target enhancement and recognition.