Analysis of Stub Loaded Circular Microstrip Antennas

Dual band circular microstrip antenna is realized by placing an open circuit stub on the edges of the patch. The stub is said to introduce capacitive and inductive impedance around the resonance frequency of the patch and realizes dual frequency response. The multi-band circular microstrip antenna is realized by placing two open circuit stubs on the opposite edges of the circular patch. In this paper, an open circuit stub loaded dual and triple band circular microstrip antennas are discussed. The analysis to study the dual and multi-band response of stub loaded circular microstrip antenna is presented. The resonance curve plots, surface current distributions and the radiation pattern plots over wide frequency range for different stub lengths were studied. It was observed that the placement of the stub modifies the fundamental and higher order mode resonance frequencies of the circular patch and realizes dual and multiple frequencies. The stub modifies the directions of surface currents on the patch and thereby gives broadside radiation pattern at first two frequencies.