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A series of comparisons are drawn between the measured impedances of skeletal wire conical (SWC) antennas and theoretical impedances obtained using the method of moments computer simulation software code (numerical electromagnetics code) NEC2 formed the basis for this study. The validity of the numerical model was established on the basis of a favorable comparison between these results; this model forms the basis for the comprehensive computational investigation of SWC antennas presented in this paper. First, a definition of impedance convergency is provided; it serves to classify SWC antennas into two groups: sparse or convergent, and convergency curves are presented. Thereafter, the geometric mean-input resistance, voltage standing wave ratio (VSWR) performance and radiation patterns of these SWC antennas are examined. Finally, four graphs are considered. Used in conjunction, these graphs provide an initial approximation of the performance/parameter characteristics of SWC antennas.

The purpose of this paper is to report on the convergence rates of two iterative matrix solution methods individually and then to combine the two methods into a hybrid scheme to achieve additional convergence rate benefits. One interative matrix solver investigated is the sparse iterative method (SIM) which is a stationary, Jacobi-like solver but uses a sparse and not a banded matrix, with matrix elements corresponding to strong interactions, rather than position in the matrix. In this paper, SIM is modified to include an adaptive relaxation scheme to improve its convergence speed and numerical stability. Another iterative scheme investigated is the nonstationary biconjugate gradient stabilized (BiCGSTAB) method. It is shown that the BiCGSTAB is considerably improved when the method is preconditioned by the sparse matrix used in the SIM method. Finally, a hybrid scheme is proposed which combines both SIM-AR and BiCGSTAB-precon and it is shown that the hybrid gives best results on the problems considered. Examples giving convergence time versus accuracy are presented for two problems: a wire-grid plate, and a wire-grid partial helicopter. Index Terms--Iterative methods, simulation software, sparse matrices.