Analysis of Broadband Variations of U-Slot Cut Rectangular Microstrip Antennas

A very popularly used technique to realize broadband and compact microstrip antenna (MSA) is by cutting a slot at an appropriate position inside the patch. More frequently, U-slot and its variation, a half U-slot, have been used to increase the bandwidth (BW). In most of the available literature on U-slot cut antennas, a detailed explanation for broadband response due to U-slot has not been reported. In this paper, an extensive study for the broadband behavior for U-slot, half U-slot and double U-slot cut rectangular MSAs (RMSAs) is presented. The U-slot configurations with different aspect ratios (i.e., length-to-width ratio) for patch and slot dimensions have been studied. In U-slot and half U-slot cut patches, it has been observed that slot does not introduce any additional mode, but it modifies the fundamental and higher order mode resonance frequencies of the patch to yield broadband response. The slot also modifies surface current distribution at higher order mode to yield broadside radiation pattern characteristics over the complete BW, without any variations in the directions of principle planes. Further, in double U-slot cut RMSA, the second U-slot optimizes the impedance and frequency at modified higher order TM21 mode and, along with modified TM01 and TM20 modes, yields increase in the BW. This paper will give an insight into the functioning of U-slot cut antennas.