Phase and Group Delays for Circularly Polarized GPS Microstrip Antennas

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

Abstract:	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 L1 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.
Published in:	Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007) April 23 - 25, 2007 Royal Sonesta Hotel Cambridge, MA
Pages:	545 - 554
Cite this article:	Dong, Weixin, Williams, Jeffery T., Jackson, David R., Basilio, Lorena I., "Phase and Group Delays for Circularly Polarized GPS Microstrip Antennas," Proceedings of the 63rd Annual Meeting of The Institute of Navigation (2007), Cambridge, MA, April 2007, pp. 545-554.
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