Three Basic Geometries of Rings Containing Microstrip Antennas

In order to obtain antennas with adjustable bandwidth, arrays based on ring antenna are used, especially for the case when it is necessary to reduce it. The arrays are formed with an inner patch designed at the operation frequency of the system, and a gap coupled external ring, designed at other near lower frequency, which determines the bandwidth increment or decrement, respectively. Three basic ring geometries were considered: circular, rectangular and pentagonal, with RT/Duroid 5880 as a substrate. The feed point is located in the inner patch, in the external ring, a shorting pin is used. The changes achieved on the bandwidth are small, but considering the used principle it remains a useful approximation, that can be improved. There were obtained a maximum increasing of 53% and a maximum decreasing of 51.44%, compared to the bandwidth of the inner patch antenna, designed at 4.9 GHz and simulated as a single antenna.