Asymptotic approximations for the mutual coupling in finite arrays of rectangular waveguides

The antenna for BRASILSAT has to operate over C-band and has to provide beams for national and regional coverages. Antennas consisting of an offset parabolic reflector that is illuminated by a reconfigurable feed array pose as a natural solution for this problem. For the array, pyramidal horns are usually employed as feed elements. In the synthesis of the excitations of the elements, the mutual coupling effects can be considered by the analysis presented by T.S. Bird (see IEEE Trans. Antennas. Propag., vol.38, no.2, p.166-72, 1990) that uses the integral equation and Green´s function approach. The analysis is centered in the calculation of self- and mutual-admittances, that involves the numerical evaluation of double integrals. In order to simplify computation, the authors introduce and asymptotic approximation in the expression for the mutual-admittance. The use of the approximate expression for the mutual-admittances is explored in the design of such antennas in conjunction with more stringent specifications for BRASILSAT