A Low-Profile Circularly Polarized Antenna With Hemispherical Axial-Ratio Beam Coverage by Dual-Mode Radiation Patterns Merging

An omnidirectional right-handed (RH) circularly polarized (CP) antenna with wide axial-ratio beamwidth (ARBW) is proposed, by which hemispherical radiation pattern coverage is achieved. The TM₁₁ and zeroth-order-resonance (ZOR) modes are simultaneously excited. The wide ARBW is formed by ingeniously merging the boresight radiation pattern generated by the inner TM₁₁ patch with the endfire omnidirectional radiation pattern generated by the outer ZOR radiator. A corporate feeding network is designed to feed the antenna. An antenna prototype is fabricated and measured. The radiation pattern covers the whole azimuth plane at 3.64 GHz and the elevation from −145° to +141° for axial-ratio (AR) < 3 dB. The measured maximum gain is 5.14 dBic at 3.64 GHz. With the hemispherical ARBW coverage and a thickness of 0.04λ₀, the proposed antenna is an excellent candidate for vehicular applications.