A method of moments formulation for small finite planar phased arrays of rectangular waveguides in an infinite ground plane is investigated. Piecewise sinusoidal-uniform surface patches are used as the basis and testing functions for the unknown equivalent magnetic currents of each aperture. The block-Toeplitz symmetry property for rectangular grid arrays is utilized in the solution of the system of equations. Data are presented for

arrays with various element sizes, element spacings, and scan angles. Good agreement with data in the literature is shown. The analysis is particularly efficient for

- plane and

-plane scans for arrays having rectangular waveguide-fed apertures excited by the dominant mode.