Numerical solution of plane wave reflection from an infinite, planar rectangular microstrip-patch array on a grounded dielectric substrate is presented and compared to phased array simulator measurements with a good correlation. In the theory, particular attention is paid to the edge condition and to the convergence of the matrix elements which was accelerated by the Poisson summation technique, as well as to the rate of convergence of the overall solution. The agreement of the values of the resonant frequencies, the associated

values, and their parametric dependence on geometry and frequency, establish confidence in the application of the method used, to prediction of performance of probe-excited microstrip-patch phased arrays.