Frequency-Reconfigurable Circularly-Polarized Omnidirectional Antenna

A concept of frequency-reconfigurable circularly-polarized (CP) antenna with omnidirectional radiation characteristics is introduced. The antenna is based on a center-fed circular patch with shorting vias, surrounded by three arc-shaped arms. Omnidirectional CP is attained through its two orthogonal radiators with a quadrature phase difference. Three varactor-loaded meandered slots are etched onto the top patch to miniaturize the antenna and empower it with reconfigurability. The resonance frequency of the vertically- and horizontally-polarized modes can be simultaneously tuned by varying the bias voltage applied to the varactors, and thus frequency-reconfigurable CP is achieved. The realization demonstrates a wide CP tuning range of 28.5% from 3.55 to 4.73 GHz. Stable omnidirectional patterns in the azimuth plane are achieved across the tuning range. All these results suggest that the antenna is suitable for communications systems that require an omnidirectional CP antenna with a frequency-tunable feature.