Numerical study of a proximity-coupled microstrip antenna with a slot

Microstrip antennas with a proximity-coupled feed enjoy a greater bandwidth as well as easier impedance matching than those with an edge feed. Slots have been introduced on the microstrip patches to improve the performance of the antennas. It has been shown experimentally that a circularly polarized small-size microstrip antenna can be designed using the proximity-coupled feed method. A cross slot with unequal slot lengths on the circular patch provides the circular polarization. On the hand, a U-slot on a rectangular patch with a coaxial feed can improve the bandwidth up to 30%. It is unclear if the bandwidth improvement can be maintained if the coaxial feed is replaced by a proximity-coupled one. We develop an efficient and flexible computer-aided design (CAD) tool for the analysis of these proximity-coupled microstrip antennas.