Optimization of Difference Pattern Sidelobes in the Presence of Fictitious Blockage

A method to improve in a particular azimuthal sector the difference radiation pattern sidelobe level of a monopulse antenna of the corporate-fed array type is presented. The technique consists of inserting a central fictitious blockage in the difference aperture distribution that has no effect on the sum mode. No excessive feed complexity or losses are introduced since the feed network is realized with only an extra power divider. The method is applied to a monopulse circular aperture with a central fictitious blockage and a prescribed aperture distribution. The relative size of the blockage is optimized to reduce the difference sidelobe level. In an example presented, the peak difference sidelobe level was decreased 8 dB along the principal plane by the introduction of a blockage that equalled one-third the aperture diameter. However, this improvement was at the expense of higher sidelobe levels in planes at azimuthal angles greater than 20° from the principal plane.