Circularly polarized GPS antenna for simultaneous LHCP and RHCP reception with high isolation

In this paper a compact dual-feed Global Positioning System (GPS) antenna for simultaneous left- and right hand circularly polarized wave reception is presented. The antenna structure consists of a single patch antenna on top of a printed circuit board and two aperture coupled feeds in the ground plane which are used to generate both left- and right-hand (LH and RH) circular polarizations for the patch. The feed network is implemented as a 2-section branch-line coupler underneath the ground plane. It is able to generate adequate phase shifts for both LH and RH circular polarizations simultaneously via two feed ports. Due to the aperture coupling and coupler implementation three layer printed circuit board approach is used. The measured axial ratio is <; 1.35 for both polarizations over the 24 MHz bandwidth at the frequency of 1.575 GHz. The isolation between the LH and RH feed ports in reception mode is -35... -26 dB in the broadside direction. The antenna enables simultaneous direct and multipath signal measurement with equal spatial coordinates for both polarizations.