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
^°
- 190
^°
, and the measured gains are observed as 3.8 dBic at θ = 0
^°
and 0.5 dBic ( - 0.5 - 1.2 dBic) at θ = 60
^°
.