Investigations on multimode microstrip patch antenna and phased arrays providing multiphase centres

The phase centre is a theoretical point along the axis of an antenna and is the centre of curvature of the phase fronts of the spherical waves. L.I. Basilio et al. (see Proc. 9th Int. Symp. on Antenna Tech. and App. Electromagnetics, p.455-8, 2002) presented investigations on defining an effective point of radiation, or phase centre, for the dominant mode of a rectangular microstrip patch antenna for Global Positioning System (GPS) applications. The determination of the phase centre and its control provides further important applications in radar systems. The paper presents the results of an investigation of a multimode microstrip patch antenna. They reveal that a single multimode patch shows a movement of the phase centre with variation in the amplitude and phase of the modes. By controlling the amplitude, the phase centre displacement is controlled, whereas by changing the phase between two modes, the direction of the phase centre movement may be controlled. The study was further extended to a finite linear array. It was seen that there is control of the phase centre movement by controlling the amplitude and phase of individual multimode patches.