Compact broadband microstrip patch antennas

We introduce microstrip patch antennas of simple shapes which can exhibit broadband operation and still enjoy relatively compact size. The circular and rectangular patches are considered when shorted to the ground plane via one or two shorting pins. The antenna is analyzed by finding the cavity modes of the structure in terms of their resonant frequencies and field distributions. Depending on the modes excited by the feeder, the patch antenna can operate as a compact antenna, as a broadband or multiband antenna. It is indicated that the suggested patch configuration can also operate as electronically tunable antenna. The theory presented here leads to universal curves for the resonant frequencies of the dominant cavity modes. The theory is supported by simulation results as well as experimental work.