Stably Polarized Wideband Circular Microstrip Antenna Excited in TM12 Mode

One of the major drawbacks of the U-slotted wideband microstrip patch antennas, i.e., the polarization instability at the high-end frequencies, is addressed by utilizing the next broadside TM₁₂ mode in circular patch antennas. The proposed antenna is capable of generating stably polarized waves over a wide frequency range of ~45% (2.05-3.25 GHz), which is not the case with the reported literature on U-slotted wideband patch antennas. The antenna comprises the U-slot and appropriately positioned shorting vias to achieve the desired impedance and radiation characteristics. It is fed by an L-probe and loaded with four non-resonating arc slits to suppress the TM₁₂ mode's E-plane sidelobes, which are very prominent otherwise. The polarization stability of the antenna is demonstrated through the surface current distributions on the patch, radiation patterns, and the x- and y-polarized gain over the frequency range of interest.