Calculation Of Frequency Responses And Poles Of UWB Radar Targets

The ultra wide-band (UWB) radar is an important development direction of modern radar system. Because of the widely expansion in frequency domain in the new radar system, much richer spectrum information of targets and environment can be obtained. Specially, features of resonance region (poles), which are only relative to physical attributes of objects, can be excited in UWB radar system. That will improve the target identification performance in the precise guidance weapon and battlefield surveillance system. So, it has importantly academic and actual significance to study on numerical calculation techniques of frequency responses and poles of UWB radar targets. Under that application background, on topics of two important features of frequency responses and poles, four parts of contents are investigated. Firstly, we study high efficient method of moments (MoM) to solve electromagnetic field integral equations, which is the numerical implement to analyze target features. Secondly, computing techniques of scattering responses in frequency domain for UWB radar targets are proposed. Then, calculation of poles of complex shaped and different material objects is analyzed. Lastly, the identification of complex targets in white or colour noise using poles' feature is studied through numerical results of frequency responses and poles.Above all, the boundary integral equations for metallic structures, dielectric structures, composite metallic and dielectric structures are elaborated uniformly based on the surface equivalence principle and boundary conditions. The solving procedures of MoM are also summarized. The higher order basis functions in MoM have many advantages to low order ones, such as fewer unknowns. So, we analyze two kinds of higher order hierachical basis functions including modified Legendre functions and power functions. On impedance-matrix filling, it is proposed that multi-dimension integrations are replaced by matrices products. The quadrature nodes and some integrated functions are calculated and stored in advance. Only Green's functions and one time low dimension matrix-vector product are to be computed each time when impedance matrix is filled. So, the matrix is fast filled. What's more, near singular process procedure is presented to increase the precision of results for irregular shaped scatterers. It is also discussed for the Schwarz preconditioner and incomplete LU decomposition with threshold preconditioner used in higher order MoM.On the aspect of calculation techniques of scattering response in frequency domain, the asymptotic waveform evaluation (AWE) and model-based parametric evaluation (MBPE) are usually used. Considering that the precision of AWE and MBPE is sensitive to sampling frequencies and the choice of frequency range, we propose Chebyshev polynomial approximation of integral nucleus in low frequency domain or resonance domain. Then, the frequency factor can be separated from integration, and only the coefficients of polynomials are relative to frequency. Other terms relative to space parameters are computed and stored. At different frequency, only the coefficients need be computed. That will largely speed up the calculation of scattering responses in a wide frequency domain. When frequency is high, the method of point-by-point should be adopted. The fast multipole method (FMM) is applied in higher order MoM on the basis of point-to-point interactions, and the particular procedure is presented. That largely accelerates the matrix-vector product in iterative process.On the aspect of calculation of poles of complex shaped and mixture objects, it is firstly reasoned that traditional contour integration is invalid for complex objects. Then, using the character of fewer unknowns in higher order MoM, the property of impedance matrix is analyzed, and the domain difference method and SVD technique to search poles are proposed. Poles of several metallic and composite metallic/dielectric target models are computed. For validate numerical results, the matrix pencil method is modified to extract dominant poles from scattering responses using frequency responses and inverse fast Fourier transformation (IFFT). The relative errors between two approaches testify the proposed methods.Lastly, the application of poles in target identification is studied. The performance of existent discrimination schemes to complex targets in white noise is analyzed. The performance of higher-order statistics for complex targets identification in the presence of colour noise is studied. The numerical results show that it is doable using the higher-order statistics to identify targets in complex background.