AMC Low Profile Wideband Reference Antenna for GPS and GALILEO Systems

Satellite positioning systems, like GPS and Galileo, require ground reference antennas with high quality radiation performance. The use of a radiator integrated with an artificial magnetic conductor (AMC) appears attractive in order to obtain an antenna with low back radiation and good axial ratio performance near the horizon, which is essential for the considered applications. The presented crossed-dipole antenna integrated on a wideband AMC has a simple feed network consisting mainly of a self balanced feed. It also has a low mechanical profile and is simple to manufacture as a multilayer printed circuit board. Detailed numerical analyses and measurements are presented which clearly demonstrate its potential as a ground reference antenna.

I. Introduction

Ground reference antennas for positioning systems, like the American GPS, the Russian GLONASS and the European GALILEO, require wide beam coverage with high quality circular polarization, low insertion loss, stable phase centre and good multipath rejection. The existing antennas take various forms including high profile antennas like helices [1], medium profile cavity backed crossed-dipole [2] and cavity backed printed antennas [3]. An additional cavity is often necessary for these antennas in order to improve their radiation performance, in particular the quality of their circular polarization at low elevation angles and their level of back radiation. In many cases a simple cavity is not sufficient to achieve the desired level of reduction of the back radiation, which is crucial to obtain a good multipath protection. Consequently large circular metallic choke rings are generally added to the antenna to reduce its back radiation to acceptable levels, which leads to bulky and heavy structures.