Wideband Microstrip Antennas Loaded by Ring Resonators

A microstrip resonator, which consists of the inner and outer square rings, is proposed for miniaturizing the parasitic elements of microstrip antennas. A pair of neighboring resonance frequencies is produced, and between them, the high impedance of the resonator is matched to the low impedance of the feedline. The impedance characteristics of the microstrip antenna loaded by one to four pieces of resonators are researched. It shows the -10-dB impedance bandwidth of the antenna is broadened from 4.7% to 10.5%, 15.5%, 15.3%, and 17.5%, respectively. The simulated and measured results prove the resonant rings loading technique is an effective method to widen microstrip antenna bandwidth.