Design of a W-band Omnidirectional Circularly Polarized Antenna by Using OMT

An omnidirectional circularly polarized (CP) antenna operating in W-band is proposed. The antenna has a simple structure, which consists of a dual-reflector antenna, an ortho-mode transducer (OMT) and a 3-dB coupler. The OMT adopts a novel septum-free structure, and can realize wideband, high isolation, and low loss. The results show that the dual-reflector antenna with this OMT has an impedance bandwidth from 91.1 to 96.8 GHz (the overlapped bandwidth limited by |S 11 | 22 |< -15dB) and a 3-dB axial-ratio bandwidth from 93.1 to 95.9 GHz. In addition, the omnidirectional CP radiation pattern can be obtained in the azimuth plane of θ = 40°- 80°.