Effect of primary feed polarization on phase centre location of parabolic reflector antennas

Knowledge of the phase centre location of the antenna is of great importance in various applications, such as global positioning system (GPS), remote sensing, radars, and virtual arrays. In parabolic reflectors, the phase centre is located at the center of the aperture plane when it is illuminated by a prime-focus point source feed having an axially symmetric pattern. It is clear that if one displaces the antenna phase centre, the apparent location of the antenna will move resulting in a virtual antenna. The virtual array antenna can be thought of as an antenna having multiple identical beams, with multiple displaced phase centre locations. Such a property is desirable in remote sensing applications, to allow multiple antenna representations. Multiple phase centre reflector antennas were studied in using a dual-mode feed horn as a primary feed. In this paper, the impact of the feed polarization on the phase centre location of offset reflector antennas will be addressed. The feed is a dual mode circular waveguide antenna operating at its fundamental mode, TEn, and the higher order mode TE21. It will be shown that the phase centre displacement can be controlled by simply changing the excitation amplitude and phase of each mode, as well as employing different mode orientations. In particular, the direction of the phase centre movement will depend on the polarization of each mode.