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 |S ₁₁ | < −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 λ ₀ ) ²  × 0.0066 λ ₀ (λ ₀ is the lowest working frequency of the antenna) are achieved for this antenna.