Analysis of slot cut multi-band rectangular microstrip antenna

Dual band rectangular microstrip antenna is realized by cutting U-slot, rectangular slot at an appropriate position inside the patch. The slot is said to introduce a mode near the fundamental mode resonance frequency of the patch and yields dual band characteristics. The triple band microstrip antenna is realized by cutting an additional slot inside the slot cut patch. It is a general understanding in these slot cut antennas that when the slot length equals either quarter wave or half wave in length then it introduces an additional mode near the fundamental mode resonance frequency of the patch and yields dual and triple band response. However it was observed in most of the cases that this simpler approximation of slot length against wave length does not give accurate result. In this paper, an analysis of half U-slot and rectangular slot cut dual and triple band rectangular microstrip antenna is presented. The slots modifies the resonance frequencies of orthogonal and higher order TM₀₁ and TM₁₁ modes of the patch and along with the TM₁₀ mode yields dual and triple band response. By studying the surface current distributions in these slot cut antennas, the formulation of resonant length at the individual frequencies is proposed. The frequencies calculated using the proposed equations agrees closely with the simulated and measured results with % error less than 5 % over the complete slot length range.