Higher Order Modes in Large-Aperture Receiving Antennas

Problems with delay distortion in a microwave relay system can result from higher order modes propagating in the waveguide feeder. Higher order modes are excited by various means in the antenna aperture. Certain higher order modes must exist in an antenna aperture to satisfy the boundary conditions of the aperture and are therefore excited by plane waves arriving on axis. These modes having on-axis lobes are found by expanding the uniform illumination function of a rectangular and a circular aperture. Higher order mode amplitudes relative to the dominant mode for each aperture shape are tabulated.