A Compact Tri-Band Horizontally Polarized Omnidirectional Antenna for UAV Applications

A compact tri-band horizontally polarized (HP) omnidirectional antenna is proposed. The HP omnidirectional antenna consists of a folded patch inside a metal box with a vertical slot. The tri-band antenna operates in the first-order resonant mode of the folded patch for the lower band, while it works in the second-order mode for the upper band, featuring a compact size of 0.32λ 0 × 0.16λ 0 × 0.08λ 0 . For the middle band, a slot mode is excited by the folded patch. Two slits on the folded patch are introduced to enhance the bandwidths of the tri-band antenna. It is shown by experiment that the tri-band HP antenna covers three frequency bands 840.5–845, 1430–1444, and 2408–2440 MHz specified by the Ministry of Industry and Information of China for unmanned aerial vehicle systems with good omnidirectionality.