A Circularly Polarized Octagon-Star-Shaped Microstrip Patch Antenna With Conical Radiation Pattern

A new circularly polarized (CP) microstrip patch antenna with conical radiation pattern is proposed and investigated. The proposed CP antenna has a single feed, a low profile, and a very simple structure. The patch has an octagon-star shape, and can be considered as a superimposition of two square patches. By generating two orthogonal degenerated TM₁₁ modes from the two superimposed square patches, omnidirectional CP radiation is achieved for the proposed antenna. The operation mechanism of the antenna is theoretically explained. A prototype of the proposed antenna is fabricated and measured. Measured results are consistent with the simulated and theoretical results. The antenna can produce a conical CP radiation pattern with a measured average axial ratio (AR) of 1.80 dB in the azimuth plane (θ = 45°) and a measured 3-dB AR bandwidth covering the global positioning system L1 band.