A Low-Profile Broadband Circularly Polarized Patch Antenna Based on Characteristic Mode Analysis

A low-profile and broadband metasurface antenna is proposed for circular polarization radiation. The metasurface is an array of subwavelength square patches. The modal behaviors of the proposed metasurface are investigated by using the characteristic mode theory. Two characteristic modes with the same resonant frequencies and orthogonal current distributions are chosen as operation modes. Furthermore, a hybrid feed system consisting of a cross-slot and a microstrip line is employed to excite the two orthogonal modes having a 90° phase difference to obtain circular polarization radiation. Based on these concepts, an antenna with low profile of 0.07λ ₀ (λ ₀ is the free-space wavelength at an operation frequency of 5.5GHz) is designed. The measurement results show that the proposed antenna has -10 dB impedance bandwidth of 4.8-6.35 GHz and 3 dB axial-ratio bandwidth of 4.85-6 GHz. Moreover, the antenna gain is 6.8-9.7 dBic in the whole axial-ratio bandwidth.