Radiation pattern analysis of arbitrary wire antennas using spherical mode expansions with vector coefficients

A spherical mode expansion with Cartesian vector coefficients is presented for the study of the radiation patterns of arbitrary wire antennas. Coefficients are obtained by using a spherical harmonic series for the free space Green's function in conjunction with the current distribution obtained with the method of moments. Transverse components of the far field are ultimately obtained yielding a compact pattern representation suitable for rapid retrieval and display. The length of the expansion is shown to be related to the precision specified for the pattern; i.e., more precision requires more terms. A useful truncation criterion is proposed and verified by comparing results obtained for several typical wire antennas. >