Dipole antennas For GPS, you need to mount the dipole horizontally However, a simple dipole mounted this way will see reflections from the ground just as well as the direct signal from the satellite This is called multipath(multiple paths that the signal can travel to get to the antenna) How do you solve the ground reflection roblem Dipole over a ground plane To solve reflection from ground problem: You make your own, highly reflective ground If the ground plane is infinite, then antenna acts like a point source in the ground plane below the antenna Gain depends on h/ In zenith h=N4 give naximum gain04/16/03 12.540 Lec 17 7 Dipole antennas horizontally problem? 04/16/03 12.540 Lec 17 8 Dipole over a ground plane h q Ground Plane Additional path 2h cosq If the ground plane is infinite, then antenna acts like a point source, in the ground plane below the antenna. Gain depends on h/l In zenith h=l maximum gain • For GPS, you need to mount the dipole • However, a simple dipole mounted this way will see reflections from the ground just as well as the direct signal from the satellite. • This is called multipath (multiple paths that the signal can travel to get to the antenna) • How do you solve the ground reflection • To solve reflection from ground problem: You make your own, highly reflective ground. /4 give 4