Numerical representation for finite arrays of rectangular waveguide apertures

A simple numerical representation for arrays of different-sized rectangular waveguide apertures has been described. The analytical expression of mutual admittance given by T.S. Bird (see IEEE Trans. Antennas Propag., vol.38, no.2, 166-72 1990) is evaluated by means of a direct integration method where the highly oscillatory integrand is locally approximated by a linear form and solved in closed form to evaluate the contribution of a single incremental area. Expressions of all applicable symmetry and reciprocity conditions have been derived. The need for using a large number of modes has also been observed. The effectiveness of the theory in predicting the performance of rectangular waveguide arrays, with closely packed elements, has been analyzed comparing measured and computed data of two different arrays. Though the numerical results denote a substantial improvement of the array modelling, the need of more accurate coupling formulas, together with the study of the scattering matrix of the horns, have to be further investigated