Performance of multimode (TE11+TE21) feed horn for offset reflector antenna providing multiphase centres

The phase centre of a feed horn is a theoretical point along the axis of the horn which is the centre of curvature of the phase fronts of the spherical waves. In most feeds, there is a phase centre region rather than a single point because radiation is due to a summation of spherical waves, which seems to emanate from the aperture [1]. Determination of the feed phase centre helps, its location relative to the focal point of the reflector. Different techniques to compute and determine the phase centre location in single and dual reflector geometries are reported in [1-3]. However, when the feed horn has a multimode excitation, the amplitude and phase control of modes provide different constant phase centre locations, which in turn helps to conceptualize a virtual array on the reflector antenna aperture [4].