Analysis of Modal Excitation in Wideband Slot-Loaded Microstrip Patch Antenna Using Theory of Characteristic Modes

In this communication, modal excitation of characteristic modes in the ultrawideband (UWB) slot-loaded microstrip patch has been investigated. A comprehensive analysis of modal excitation due to straight and L-probe feed reveals physical insight about antenna behavior due to feeding structure. This communication analyzes the modal effect of feed inclusion in two steps, i.e., before and after excitation. The application of characteristic modes to antenna bandwidth enhancement serves as a demonstration of the broad utility of the theory of characteristic modes (TCM), where multiple resonant modes participate simultaneously to broaden the bandwidth. This communication also examines the potential capability of natural resonant modes to contribute to the impedance bandwidth upon excitation. The slot-loaded antenna exhibits 35% impedance bandwidth with the straight probe feed, but bandwidth increased up to 81% by changing the feed to L-probe. Hence, impedance bandwidth has been enhanced up to 46% (approx) by exciting particular resonant modes via changing and optimizing a feed structure.