High-Gain Omnidirectional Circularly Polarized Array Based on Folded Counter-Wound Helix

A high-gain omnidirectional circularly polarized (OCP) helical array is reported in this letter. It consists of four identical OCP folded counter-wound helices that are parallel-fed by an equal-split power divider structure. The counter-wound helix's folding technique features a high radiation resistance of 102.1 Ω and a compact size of 0.055 × 0.055 × 0.39
λ
₀
³
, thus achieving good matching and alleviating the mutual coupling of the shunt-fed array. A prototype is fabricated and tested. Measured results indicate that the array achieves an impedance bandwidth (|S
₁₁
| <10 dB) of 2.35–2.42 GHz (2.94%) and a 3 dB axial ratio bandwidth of 2.32–2.45 GHz (5.4%). The proposed array exhibits omnidirectional properties with a maximum measured overall gain of 7.9 dBic throughout the operating band. The total size of the array including the feeding network is 0.11 × 0.53 × 3.3
λ
₀
³
.