Omnidirectional Circularly Polarized Antenna Array With Planar Configuration

A compact omnidirectional circularly polarized (OCP) linear antenna array with a planar configuration is presented in this communication. By using the cavity model, a shorted half mode patch antenna is analyzed, where the TM modes are taken into consideration. The periodical reversal of the structure at the null point of the higher order mode produces an equivalent long magnetic source array (LMSA) at the open aperture based on the duality principle. Meanwhile, rectangular plates are periodically introduced at the junction of two adjacent cells on the upper or lower surfaces, on which lateral current is generated along the same direction that realizes an equivalent long electric source array (LESA). As a result, two naturally parallel arrays, which are the LMSA and the LESA, are obtained and integrated into a compact format. With the equal magnitude and an inherent 90° phase difference, the two array sources could generate an OCP radiation. Furthermore, a matching network is utilized to expand the impedance bandwidth. Ultimately, a planar $1 \times5$ OCP antenna array is fabricated and tested to verify the design. A −10 dB impedance bandwidth of 8.1% (5.35–5.8 GHz) and a peak LHCP gain of 4.6 dBic are achieved. Good OCP radiation patterns are obtained across the operation band.