An ultra-wideband 12-elements omnidirectional antenna with compact size and low gain variation

Abstract

This letter provides the design of a planer ultra-wideband horizontally polarized (HP) omnidirectional antenna. To obtain the omni-directional radiation performance, a circular array composed of 12 Vivaldi units is proposed. And a 1-to-12 ultrawideband power divider is designed to achieve ultra-wide impedance matching bandwidth. The antenna is designed and measured with bandwidth of 134.3% (1.96–9.98 GHz) for |S11| < −10 dB. And a qualified omnidirectional radiation performance with gain variation ≤3 dB is achieved over the frequency of 1.96–8.1 GHz. Meanwhile, the peak gain of 3.42 dBi and a compact size of π × (0.43 λ0)² × 0.0066 λ0 (λ0 is the lowest working frequency of the antenna) are achieved for this antenna.