Compact Circularly Polarized Antenna With Wide 3-dB Axial-Ratio Beamwidth

A compact circularly polarized antenna with wide 3-dB axial-ratio (AR) beamwidth is presented. The two pairs of radiators based on mu-negative transmission lines are applied and each radiator has a capacitor at the center and a pair of vias at both edges of the radiator to induce a zeroth-order resonance mode. The two radiators for x-polarized wave are orthogonally aligned to the other two radiators for y -polarized wave, and the 90 phase difference is realized by detuning the resonance frequencies of the corresponding radiators. In particular, a circular ground plane is adopted for the symmetrical radiation pattern and optimized to have the wide 3-dB axial -ratio beamwidth. Also, a dual -ground structure is studied to suppress back radiations caused by the compact ground. The 3-dB AR beamwidth is measured as 175 degrees - 190 degrees, and the measured gains are observed as 3.8 dBic at theta = 0 degrees and 0.5 dBic (-0.5 1.2 dBic) at theta = 60 degrees.