Observation of two counter-intuitive behaviors in the antennas having EBG or HIS structure as the ground plane

Abstract

Advantages of employing artificial ground planes such as electromagnetic band-gap (EBG) structures, high impedance surfaces (HISs) and artificial magnetic conductors (AMCs) for different antennas has received much attention for almost a decade, since their introduction in [1]. It has been illustrated in [1], that EBG structures suppress surface waves propagating transversely along the ground plane [1]. When such structures are used as the antenna ground planes, due to the absence of the surfaces waves, it is expected that less power is wasted in the backward radiation or edge diffractions and thus the antenna directivity is increased. For the HIS or AMC ground planes, on the other hand, image theory is invoked to explain the efficient antenna radiation. As is known, a horizontal wire radiates poorly above the conventional ground plane, commonly made of a good electric conductor, due to the reverse image introduced by the ground plane. Using a magnetic ground plane, one expects that this problem to be alleviated significantly because of the in-phase flowing currents in the wire and its image. The magnetic conducting ground planes in practice are artificially simulated by the so-called HISs or AMCs, which are typically periodic structures [1].