Analysis of nearly cylindrical antennas and scattering problems using a spectrum of two-dimensional solutions

This paper presents a powerful method for analysing antennas which can be considered principally two-dimensional (2-D) or cylindrical, except for some three-dimensional (3-D) physical or equivalent sources, e.g., dipoles or slots. It is shown by Fourier transform techniques that such antennas can be analyzed as 2-D problems with harmonic longitudinal field variation. The radiation pattern can often be determined directly from a finite set of such 2-D solutions, each one obtained by any method, e.g., the moment method. The mutual interaction between the cylindrical scatterer and the sources must be calculated to determine the exact current distribution on the sources and their impedances or admittances. This is facilitated by performing an inverse Fourier transform of an infinite spectrum of the numerical 2-D solutions followed by a moment method solution in the spatial domain to satisfy the boundary conditions on the 3-D equivalent sources themselves. The inverse Fourier transform is simplified by the use of asymptote extraction. The method is in itself a hybrid technique as one method is used to solve the harmonic 2-D problem, and the other to solve for the source currents.