Multiple Phase Center Performance of Reflector Antennas Using a Dual Mode Horn

A new application for reflector antennas is proposed and developed. Using the aperture theory, a phase center on the reflector aperture is determined and shown that, its location is dependent on the field distribution. The proposed concept is, initially, verified by using a symmetric reflector. It is shown that the phase center is located at the aperture geometric center, when the reflector is illuminated symmetrically about its principal planes. Then, a dual mode feed, employing TE₁₁ and TM₀₁ modes, is used for generating different reflector illuminations, and causing displacement of its phase center. The concept is then extended to offset reflectors, and the influence of the reflector geometry on the phase center displacement and other reflector electrical parameters is investigated. Based on the established feed radiation pattern requirements, a feed horn is designed using circular waveguide that can propagate both modes. By modifying the amplitude and phase of the modes in the horn, a controlled asymmetric reflector aperture field is achieved. A prototype feed horn is fabricated and tested for its dual mode radiation patterns. The results are in good agreement with simulations. The reflector phase center properties are then investigated, by using the designed feed. A reflector-feed assembly, with its dual phase center capability, was developed for improving the performance of the ground moving target indicator radars. The concept allows the conversion of a single reflector to two or more reflectors, simply by modifying the mode excitation amplitudes and phases, in the feed alone