Publications Details

Phase and group delays for circularly polarized GPS microstrip antennas

Dong, Weixin; Williams, Jeffery T.; Jackson, David R.; Basilio, Lorena I.

The antenna element in a GPS receiver is a source of positional errors that need to be accounted for in moderate-to-high precision GPS systems. In this paper the phase and group delays are calculated for common circularly-polarized (CP) microstrip (patch) antenna designs. The phase and group delays are calculated using a theoretical cavity model as well as an accurate finiteelement electromagnetic simulator (Ansoft HFSS). Results for right-handed circular polarization (RHCP) antennas fed in two different ways are explored: an orthogonal-feed antenna and a diagonal-feed antenna. All results are for operation at the Ll frequency (1.575 GHz). It is shown that the group delay is much larger than the phase delay, due to the high-Q nature of the patch antenna (low bandwidth). Of particular interest is the variation of the phase and group delays with observation angles, since this translates into delays that will be different for each satellite signal, and hence directly corresponds to a positional error.