Analysis of stub loaded equilateral triangular microstrip antennas

The dual band microstrip antenna is realized by placing the open circuit stub on the edges of the patch. While designing the patch for desired dual frequencies, the stub is taken to be nearly quarter wave in length. However this simpler approximation does not give closer results for different stub lengths. In this paper, the dual band response of stub loaded equilateral triangular microstrip antenna is studied. The resonance curve plots, surface current distributions and radiation pattern plots were studied over wide frequency range. It was observed that the stub modifies the fundamental and higher order modes of the patch and realizes dual frequency response. The placement of stub alters the directions of the surface currents on the patch and therefore gives similar radiation pattern characteristics at the dual frequencies. By studying the surface current distributions a formulation of resonant length at the dual frequencies in terms of the stub dimensions is proposed. The frequencies calculated using them closely agrees with the simulated results with a % error of less than 5%.