Abstract: An antenna having a rotatable phase center is disclosed. The antenna includes a horn antenna having a phase center and at least one rod-like impedance element located adjacent a wall of the horn antenna near the phase center. The length of the impedance element is selected such that it shifts the phase center from its normal, undisturbed location without substantially affecting the amplitude pattern of the antenna. Means is provided for mechanically rotating the rod-like impedance element around the phase center so as to thereby cause the phase center to also rotate.

Abstract: An antenna (50) is disclosed herein whose phase center may be electrically moved relative to a main receiving/radiating element. The main receiving element (56) is located in a cavity (54) in a ground plane (52). Spaced around the main receiving element are a number of paracletic elements (58, 60, 62, 64), each of which has at least two switchable reactance states. In one state, there is little coupling between the paracletic element and the main receiving element. In another state, coupling is increased so that the phase center of the antenna shifts towards the paracletic element. A sequencer (100) supplies bias voltages to switching diodes (84, 86) to control the reactance states of the paracletic elements and thus the position of the phase center of the antenna. The antenna may be used as a tracking feed (14) for a directional lens or reflector system (12).