Study And Application Of Hybrid Low/High-Frequency Method

Electromagnetic characteristics analysis of antennas and targets, as an importantbasic technology in the radar science, not only is on the subject front, but also hasoverall, fundamental and pioneering properties.Therefore, study on electromagnetic characteristics of antennas and targets hasalways been of concern. In the electromagnetic community, the research has been putforward under the background of various engineering requirements, and supported bythe ongoing financial allocations. Conversely, scientific achievements including thetheoretical prediction methods, measurement data and computer code for analyzingelectromagnetic characteristics have been widely used in industry. Being associatedwith the National Natural Science Fund and a number of research projects, thisdissertation mainly focuses on the hybrid method research based on the electric fieldintegral equation (EFIE), and combines this algorithm with the current internationalmainstream frequency sweep technique so as to realize the fast analysis of broadbandelectromagnetic system. The major contributions in this paper are summarized asfollows:1. The method of moments (MoM) based on the EFIE is introduced in detail,which has been applied to analyze the electromagnetic scattering of perfectly electricconducting (PEC) and homogeneous dielectric targets. On the other hand, the discreteequation is obtained by using pulse vector basis functions which are defined on theplane triangles. This practice can make the calculation of impedanceelements be a single integral and the computational complexity low. It is wellknown that the computing resources are usually insufficient when MoM is used to solveelectrically large problems. To alleviate this difficulty, the integral equation-fast Fouriertransform (IE-FFT) is studied and the algorithm processes are presented. Comparedwith the conventional MoM, the IE-FFT method has advantages in memoryrequirements and solution time.2. The IE-FFT is utilized to accomplish radiation analysis of antennas aroundconducting platforms using surface-surface configurations. This simplified algorithmdecreases the complexity of the impedance matrix caused by wire-surface basisfunctions, and also facilitates the solution of large problems.3. The method of moments and physical optics (PO) hybrid principle,formulationand process are studied. For PO theory can not handle edge diffraction field andcurrents in the shadowed region, the equivalent electromagnetic currents (EEC) and non-uniform grid methods are employed to modify the conventional MoM-PO,respectively. Several examples are given in this paper to prove that the modified methodcan acquire more accurate results than the conventional MoM-PO.4. An efficient hybrid analysis that combines integral equations with physicaloptics approximation is proposed for antennas around an electrically large platform. Inthe analysis, the whole surface of the platform and antennas is divided into two regions,namely, the full-wave region and the PO region. In the full-wave region, the integralequation is modified by coupling into the PO contribution. By interpolating the Green’sfunction on a regular Cartesian grid, the impedance matrices can be stored in sparseformat, and the matrix-vector multiplications can be accelerated by fast Fouriertransform.5. An efficient wide-band analysis that combines MoM-PO hybrid formulationwith the asymptotic waveform evaluation (AWE) technique is proposed for antennasaround an electrically large platform. Compared with the frequency sweeping techniquebased on MoM, the MoM-PO hybrid formulation is employed to reduce the number ofunknowns in the matrix equation. Further, the automatic differentiation (AD) approachis used to calculate the high order frequency derivatives of Green’s function. Numericalresults show that the presented method can achieve considerable reduction in solutiontime without loss of accuary.6. The IE-FFT algorithm combined with the best uniform approximation is appliedto analyze the scattering of an arbitrary shaped perfectly electric conductor over a widefrequency band. The basic idea of the method is to approximate the frequency responseby a low-order rational function. Therefore, a relatively small set of Chebyshev nodesare extracted to represent a large network that may contain a number of actual nodes.Compared with AWE, the best uniform approximation does not need to compute thehigh derivatives of the impedance matrix which results in that the technique is apractical frequency sweeping algorithm. On the other hand, MoM-PO hybrid method inconjunction with Maehly approximation technique is applied to the wide-band analysisof antennas around an electrically large platform. Finally, the computational accuracy, memory requirements and solution time of different approaches are deeply analyzed inthis paper.