Effects of the Rooftop Environment on GPS Time Transfer

Michael A. Lombardi, Andrew N. Novick

Abstract:	We examine the effects of the rooftop environment on GPS time transfer, in particular the effects of multipath reflections from nearby metallic objects. Three different antenna sites on the roof of the NIST laboratories at Boulder, Colorado, were selected, each with different multipath characteristics that we discuss. Simultaneous tests were conducted at each site with the same model of L1 band GPS receiver, but with different types of antennas. Four different types of active antennas with low-noise amplifiers were used at each site: a patch antenna, a patch antenna with a simple choke ring attached, a quadrifilar helix, and a “pinwheel” antenna with an aperture coupled slot array design. Results are presented that demonstrate how each antenna performs in each multipath environment, with the time deviation (sx(t)) used as a metric. We also discuss the potentially harmful effects on time transfer caused by RF interference from other active GPS antennas located on the same roof
Published in:	Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 2006 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	449 - 466
Cite this article:	Lombardi, Michael A., Novick, Andrew N., "Effects of the Rooftop Environment on GPS Time Transfer," Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2006, pp. 449-466.
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