Efficient Computation Of Green’s Functions In Cylindrically Stratified Media

As the simplest conformal strucuture, cylindrical surface has received more andmore attention. Now, cylindrically conformal antennas have been widely applied inpractice. However, until now, there has no efficient and accurate analysis method forthis type of structure, the efficiency of the commercial software for electromagneticsimulation is not very satisfying. Due to this situation, in this thesis, an efficient andaccurate method, which is based on the method of moments (MoM) combined with thelayered Green’s functions for cylindrically stratified structure, is studied exhaustivelyand systematically.First, to overcome the problem in the literature for deriving the formula of theelectric dyadic Green’s functions (EDGFs) for cylindrically stratified structure, such asthe incomplete equations, the unclear definitions, and the complicated derivation, theexplicit formula of EDGFs is thoroughly rederived, which provides a foundation for thefollowing study.In order to avoid possible overflow/underflow problems in the numericalcalculations of EDGFs for cylindrically stratified media, the explicit expressions of thecomponents of EDGFs are rewritten in the ratios of Bessel and Hankel functions, whichavoids directly calculating Bessel and Hankel functions with high order and largearguments. Compared with other method, the procedure in this thesis is simpler, andeasier for programming and application.In order to further improve the accuracy and efficiency of the numerical method inthe calculation of the components of EDGFs in spatial domain. A surface-waveextraction method based on the rational function fitting method (RFFM) is proposed.The method can calculate both the near and far field of the components of EDGFsefficiently and accurately. The accuracy range between the source and field points isincreased by about one order, which can enhance the ability for analyzing theelectrically large antennas mounted on cylindrical surface.In the analysis of cylindrically stratified structure, in order to make use of theRWG basis function in the MoM procedure, the mixed potential dyadic Green’sfunctions (MPDGFs) for cylindrically stratified media are further studied in this thesis.Two different forms of MPDGFs reported in the literature are rederived anddemonstrated. Meanwhile, the RFFM is extended to calculate the far fields of thecomponents of MPDGFs.From the literature, it is found that the method proposed for the calculation ofspatial-domain MPDGFs can not be valid when the source and field points are locatedon the same axial line, which will make the MoM Procedure more complex. In order toovercome this problem, a two order analytical asymptotic term extraction method is proposed in this thesis. In this method, the singular parts related to the axial line arecompletely extracted, and then transformed into the spatial domain with the aid ofSommerfeld identities. After this extraction, the remaining parts in the spectral domainare fast convergent and can be easily transformed into the spatial domain using thenumerical method such as the generalized pencil of function method (GPOF). Unlikethe other method, this method need not choose special basis functions to cancel thesingularity in the spectral-domain MPDGFs. The performance of convergence andstability are significantly improved.At last, based on the above study, the MoM procedure combined with the roof-topbasis function is applied for analyzing dipole and rectangular antennas mounted on thecylindrical surface. The input impedance, surface current, radiation pattern and themutual coupling coefficients between antenna array elements are calculated. Incomparison to the results obtained by other algorithms and the simulation software, it isdemonstrated that the method in this thesis has a good performance of accuracy,efficiency and easy applicability.The procedure introduced in this thesis will provide a possibility for analyzingcylindrically conformal antennas more efficiently and accurately.