Low-Profile, Switched-Beam Diversity Antennas Using High-Impedance Ground Planes

We explore high-impedance surfaces for use in low-profile, switched-beam diversity antennas for mobile communications. High-impedance surfaces provide two important advantages for low-profile antennas: (1) They suppress the propagation of surface currents. (2) Image currents appear inphase, rather than our-of-phase as on an ordinary metal ground plane. This results in improved radiation properties by partially isolating the antenna from the nearby electromagnetic environment. Furthermore, radiating elements can lie directly adjacent to the ground plane without being shorted out. A low-profile, four-sector diveristy antenna on a high-impedance surface is described, and radiation performance is characteriazed.