Low profile antennas and arrays for satellite navigation

The Global Positioning System (GPS or Navstar) is a highly accurate navigational aid, which relies on receiving circularly polarised signals at 1575 MHz (L1) 1227 MHz (L2) from a number of satellites scattered across the upper hemisphere. The signal bandwidth is 20 MHz at both L1 and L2, with a relatively flat pass band response, so that the 3 dB bandwidth of the antenna is significantly greater than this (50-100 MHz). The antenna radiation pattern needs to be very broad, maintaining good coverage close to the horizon. For aircraft applications in particular, a low profile antenna is required, suggesting a printed or cavity backed approach. A single printed patch antenna can give circular polarisation on axis, and a uniform pattern in azimuth, but does not have a sufficiently broad elevation pattern