Method of reducing mode-degeneracy problem in annular-ring patch antennas

The annular-ring patch antenna with an extended ear at its outer periphery is analysed. A mode matching technique (MMT) is utilised and is improved by incorporating the mutual coupling effect between the two radiating edges. The formulations for the wall admittances including the extended ear are also developed. The analysis shows that for an annular bandwidth of the TM12 mode is increased by increasing its inner radius. It also moves the resonant frequency of the TM02 mode towards that of the TM12 mode, overlap-ping their bandwidths and causing mode degeneracy. The addition of an extended ear separates the mode resonances and removes their degeneracy and, therefore, the usable range of frequency for a particular mode is increased. An annular ring with the extended ear is fabricated and tested. The numerical results of the improved MMT agree more closely with the experimental data than those obtained using the conventional MMT used in the literature.