A Novel Characteristic Mode Method to Enhance Axial-Ratio Bandwidth of Low-Profile Circularly Polarized Planar Antennas

A novel characteristic mode (CM) method for enhancing axial-ratio (AR) bandwidth (BW) of various low-profile circularly-polarized (CP) planar antennas is proposed. The basic idea of the modal method is to introduce a new CM, and then to properly adjust both its resonant frequency (ResF) and polarization, resulting in making full use of such two degrees of freedom. To demonstrate the modal method, a CP slot antenna is proposed and its 3-dB AR BW is effectively enhanced from 5.1% to 11.8%. A prototype for the enhanced CP slot antenna is fabricated and measured for experimental validation.