Compact Omnidirectional Antenna of Circular Polarization

A compact omnidirectional antenna of circular polarization (CP) is presented for 2.4-GHz WLAN access-point applications. The antenna consists of four bended monopoles, which are simultaneously excited through an associated feeding network. The radiated horizontal and vertical field components are derived based on an analytical model, and the 90^° phase difference between them is shown to be naturally guaranteed. With a size of 0.22λ₀ × 0.22λ₀ × 0.076λ₀, the antenna exhibits a bandwidth (|S₁₁| ≤ -10 dB and AR ≤ 3 dB) of 3.56% and a left-handed CP average gain of 1.39 dB in the azimuth plane at 2.44 GHz.