Antennas on High Impedance Ground Planes: On the Importance of the Antenna Isolation

Abstract

Photonic Band-Gap materials (PBG) are periodic structures composed of dielectric materials or metal. They exhibit frequency bands for which no propagation mode can propagate. Unfortunately, they are bulky and their period has to be at least a quarter wavelength. One extension of the PBG structures is called High impedance ground planes (High Z). Their period is much smaller and they exhibit frequency bands in which no surface wave can propagate. Their electromagnetic characteristics make them particularly interesting for antenna applications. On the one hand, they reduce the interaction between an antenna and its backward surroundings, with smaller size than usual ground planes. On the other hand, they can be used for planar antenna solutions, as the radiating element can be placed right on the top of the ground plane. After a presentation of the steps which lead to High Impedance ground planes, the electromagnetic characteristics of such ground planes are presented. Then, some antenna applications illustrate the interest of such structures. 1 High Impedance Ground History 1.1 Photonic Band-Gap Materials 1.2 Metallo-Dielectric PBG 1.3 High Impedance Ground Planes 2 Electromagnetic Characteristics of High Impedance Ground Planes 2.1 Corrugated Surfaces 2.2 High Z Equivalent Circuit Model 2.3 High Z Electromagnetic Characteristics