Singly-Fed Circularly Polarized Circular Aperture Antenna With Conical Beam

A singly-fed circular aperture antenna radiating left-hand circularly polarized conical beam is proposed. The circularly polarized characteristic is realized by exciting ${\rm TM}_{01}$ and ${\rm TE}_{01}$ modes in a circular waveguide simultaneously. Through optimized design, the antenna provides an impedance bandwidth $(\vert {\rm S} _{11} \vert < -10~{\rm dB})$ of 5%, from 12.15 to 12.8 GHz, and an axial ratio bandwidth $({\rm AR}< 3~{\rm dB})$ of 4.8%, from 12.2 to 12.8 GHz. At the central frequency 12.5 GHz, a flare angle of 28 $^{\circ}$ of the radiation pattern and a measured gain of 7.5 dBic have been achieved. Good agreement has been observed between simulated results and measured ones.