Analysis of shorted-plate compact and broadband microstrip antenna

A broadband configuration of a shorted-plate folded L-slot-cut folded-feed rectangular microstrip antenna was reported, which gave a bandwidth of 2840 MHz (133%). The broader bandwidth was obtained due to the coupling between various modes, which were either a half-wave or a quarter-wave in length. However, a clear description of the modes of the shorted patch that resulted in the broadband response was not given. In this paper, an analysis studying the broadband response of the reported configuration is presented. By studying the voltage and current distributions on the shorted patch, a formulation for its resonance frequency is proposed. The frequencies calculated using the proposed equation closely agreed with the simulated results. Furthermore, the broadband response of the reported configuration was analyzed by studying its resonance-curve plots and surface-current distribution. It was observed that the folded patch and a wing-like extension on the folded-patch portion, the L-slot, and the folded feed modified the various fundamental and higher-order mode resonance frequencies (such as f_1/4,0, f_1/4,1, etc.), as well as the impedances at these frequencies, to yield the broadband response. Furthermore, by optimizing the folded feed length, an increased bandwidth of 3504 MHz (139.2%) was obtained. Over the bandwidth, this configuration showed a radiation pattern with higher cross-polarization levels and with a gain of more than 5 dBi.