Radar Target Features Extraction And Target Indentification In Resonance Region

Radar target scattering characteristic in resonance region which takes the shape and size principle information of target is the most efficient spectrum characteristic for radar target identification (RTI). Ship and airplane targets locate in the resonance region for the working frequency of high frequency surface wave radar (HFSWR). This feature is the foundation of HFSWR target identification. Conducting the radar target identification research in resonance region can realize early stage warning and effective tracking and attack to major targets, exploit the advantage of HFSWR and improve the system performance of the HFSWR. According to this research background, research is carried out in three aspects which is radar target scattering characteristic analysis, aspect independence radar target feature extraction and HFSWR target identification.Firstly, surface geometry modeling method is used to replace wire-frame geometry modeling method in method of moments (MoM) based radar cross section (RCS) simulation. A modeling method based on the finite element modeling and post-processing software (FEMAP) which is fit to the resonance region targets is proposed in detail. Furthermore, a calibrating RCS approach utilizing the first order sea clutter to decrease the offset which is produced by the inaccurate of Norton surface wave attenuation and antenna gain is given to obtain more accurate measured RCS. Comparing with the measured RCS from HFSWR system, Simulation RCS results using these surface geometry modeling methods is more precise than the result of wire-frame geometry modeling method. Ship and airplane target RCS change characteristics are given and influences of target dimension and classic parts on the RCS are also analyzed based on the plenty of simulation results.Secondly, problems in complex target natural resonance frequencies (poles) extraction from MoM-based simulation frequency domain scattering data are investigated. A complex target poles extraction method exploiting simulated scattering data in frequency domain is provided. Waveform extended process due to the limited frequency band is analyzed and its influence to the transient response in time domain is also studied. More reasonable beginning time of late time response is defined. Then a modified total least square matrix pencil method (MTLS-MPM) is proposed to remove the disturbance of poles number uncertainty along with calculation errors based on minimal reconstruction error of late time response. Thus reliable poles extraction is realized, and poles location in complex plane of ship and airplane targets are first presented which is coincident in different aspects. Therefore, transient response is reconstructed by few pairs of pole and residue, and target frequency domain response is represented by poles and residues for the first time.Rational approximation to the target frequency response data is studied to obtain the target feature and accurate frequency response approximation. Least square rational approximation method and mini-max rational approximation method are investigatied. However, shortcomings of normal equation matrix ill-condition along with linearization error are discovered in theoretical analysis and numerical simulation. A rational approximation method based on orthogonal vector fitting (OVF) technique is proposed. Central to this method is that orthogonal partial fraction, instead of polynomial, is adopted as basic function of denominator and numerator to improve numerical stability, and iteration is used to decrease the linearization error. Simulations of simple and complex targets show that excellent approximations to frequency response are achieved. In addition, poles location is accurate as well as aspect independent. Particularly, Results of simple target poles are more precise than results of MTLS-MP.Finally, RTI in resonance region is studied. Target identification exploiting poles extraction and matching is investigated in broadband radar. Influence of noise in measured response on the poles extraction and target indentification are also studied. In narrow band radar target identication, research is emphasized on radar working frequency selection so as to improve multi-frequency radar target identification performance. Frequency optimal section based on minimal error rules (MER) of classification is proposed which can increase the identification probability without added frequency number. An expanded nearest neighbor (NN) classification method is given to realize the fundmation of rejection.