| In recent years, with the rapid development of radar detecting systems and stealthtechnology, electromagnetic scattering analysis of targets has ever-increasing demands. Incomplicated electromagnetic environment, antennas for wireless telecommunications andnavigations are usually mounted on aircraft, naval ships, tanks and missiles. The performanceof antennas is not only determined by antennas themselves, but is also determined by theplatforms. Therefore, in modern electromagnetic engineering, the research on analysis ofelectromagnetic scattering of targets and radiation of antennas mounted on platforms hasgained much attention. Being associated with the research projects, this dissertation mainlyresearches on the method of moments and its fast algorithm, i.e. adaptive integral method, andthen these methods are employed to wide-band analysis of electromagnetic scattering oftargets and radiation of antennas mounted on platforms. The author’s main contents and majorcontributions are outlined as follows:1. The method of moments (MoM) based on electric field integral equation (EFIE),magnetic field integral equation (MFIE) and combined field integral equation (CFIE) isstudied in detail. The computational accuracy, applicable area, advantages and disadvantagesof these three surface integral equations are deeply analyzed. The memory requirement andcomputational complexity of MoM are too large. To alleviate this difficulty, the adaptiveintegral method (AIM) is developed based on these three surface integral equations, and amethod is proposed to store the sparse matrices in compressed format. Then the memoryrequirement and the computational complexity are reduced toO N32andO N32logN orless.2. The adaptive integral method is utilized to solve electromagnetic radiation propertiesof conducting surface/surface configurations. For a complex structure that involves wires andsurfaces, a special basis function must be introduced to deal with the rapid varying currentdistributions. To simplify this model, a uniform RWG basis function has been used to modelthe surface/surface junction by using a thin strip with no thickness instead of a wire. And thenthe AIM is employed to reduce matrix storage and to accelerate the matrix-vectormultiplications in the iterative solver.3. A novel Gauss interpolation operator is presented to obtain the grid potentials in theAIM implementation. Compared with the conventional AIM, the major advantage of Gaussoperator is that it can avoid computing the inverse of Vandermonde matrices for x, y, z 4. In order to implement fast monostatic RCS computation over a given angle band orRCS computation over a given frequency band, the hybrid method which combines the AIMand asymptotic waveform evaluation (AWE) technique is studied. The EFIE is used toformulate the problem and the MoM is employed to solve the equation. By using the AWEtechnique, the unknown equivalent current is expanded into a Taylor series around a givenangle in the desired angle band or a given frequency in the desired frequency band, and thenarbitrary angle or frequency in the angle or frequency band can be obtained via the Padéapproximation. The AIM is used to reduce the impedance matrix and its frequency derivativesmatrices storage and accelerate all the matrix-vector multiplications in the linear systems forthe coefficients of the Taylor series. Compared with the point-by-point AIM simulations, thehybrid method can achieve considerable reduction in computational time without loss ofaccuary.5. The AIM is combined with the AWE technique to present wide-band analysis ofantennas mounted on platforms. The symbolically differentiation is difficult to obtain thehigh-order derivatives and to implement. The divided differences will introduce the round-offerrors in the discretization process. To alleviate these difficulties, the forward mode automaticdifferentiation (FMAD) technique is proposed for calculating the high-order frequencyderivatives of Green’s function. Then the localized SBI preconditioner is employed to reducethe iterative numbers of the linear systems for the coefficients of the Taylor series, whichfurther speeds up the algorithm. Finally, the computational accuracy, memory requirementand computational time of four different orders of the AIM-AWE method are analyzed.6. A novel current-based hybrid method which combines the AIM with the physicaloptics (PO) is proposed for analysis of radiation problem of antennas around platforms. In theanalysis, the whole structure is divided into two regions, namely, the MoM region whichincludes antennas and the PO region which includes platforms. The coupled EFIE equationbased on the MoM region is established by considering the PO contributions. The AIM isused to reduce the impedance matrix in MoM region and the interaction matrix between MoM region and PO region and to accelerate all the matrix-vector multiplications in the coupledEFIE. |
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