A Cross-Polarization Reduction of a Cavity-Backed Patch Antenna Using the Characteristic Mode Analysis and SISL Technology

The cross polarization (Xpol) in rectangular patch antennas is studied using the characteristic mode analysis (CMA). In exciting the fundamental mode (TM01) of the rectangular patch, the CMA evinces that the high H-plane cross-polarization is due to asymmetry by the feeding structure, which excites the unavoidable undesired higher-order mode (TM20). Based on the revelation by the CMA, a parasitic loop is proposed to suppress the TM20 mode by shifting it to a higher frequency band with remarkable Xpol reduction. The proposed antenna is implemented using the SISL technology in the S-band with consistent H-plane Xpol reduction. A full range of elevation angles of Xpol reduction from 17.9 to 22.8 dB is achievable in the H-plane across the desired bandwidth. The antenna is fully planar, easy to integrate, and maintains high performance applicable to conformal arrays.