Wideband Dual Circularly Polarized Antenna for Intelligent Transport Systems

A wideband dual circularly polarized (DCP) antenna is presented for intelligent transport system (ITS) applications, which can be used to improve the receiver sensitivity and communication quality of ITS. The presented DCP antenna is composed of an orthogonal power divider (OPD) with two orthogonal input ports, four phase shifters for quadrature phase output, and four crossed dipoles for DCP radiation. Detailed equivalent circuit analysis shows that the OPD has two orthogonal inputs and four equal magnitude in-phase and out-of-phase outputs. To achieve two sets of orthogonal quadrature output signals for DCP radiation, the lumped element based differential right-hand transmission line unit cell and left-hand transmission line unit cell are elaborately introduced as the ±45° phase shifters, and incorporated into the OPD. Eventually, orthogonal quadrature signals are successfully obtained and fed to the crossed dipoles for DCP radiation. The proposed antenna was then designed, fabricated, and measured for ITS applications. The measured results show that the overlapped impedance bandwidth of both two input ports is 1.07–1.85 GHz (53.4%), and the isolation is higher than 15.2 dB. Moreover, low axial ratio (<1.7 dB) and symmetrical radiation patterns are achieved for unidirectional DCP radiation.