Minor lobe suppression in a rectangular horn antenna through the utilization of a high impedance choke flange

A significant reduction in the minor lobe radiation pattern of a rectangular pyramidal horn antenna is obtained by placing a choke around the aperture of the antenna and adjusting the choke to approximately a quarter wave in depth. The reduced minor lobe radiation means less scattering and a higher efficiency. The choke also results in an improvement in the antenna gain with a measurably narrower beam. A minor variation of approximately 10 percent, peak to peak, is obtained in the antenna input impedance for choke depths varying from zero to a quarter of a wave.