Directivity Enhancement of Printed Antennas Using a Class of Metamaterial Superstrates

Abstract

In this paper, we present some applications of metamaterial superstrates for directivity enhancement of printed antennas. Three different types of superstrates, viz., multilayer dielectric slabs, electromagnetic band gap (EBG) materials, and frequency selective surfaces (FSSs) are discussed. We first present the design of a multilayer dielectric slab, consisting of high and low permittivity dielectric layers and air-gap tuners for suppressing the grating lobes of patch array antennas. Next, a dielectric-rod EBG-type superstrate with two defect frequencies is proposed for dual-band directivity enhancement of a patch antenna at a boresight. With this design we can increase the degrees of freedom that adjust the level of directivity enhancement and operating frequency location, relative to those of the multilayer dielectric slab type. Finally, an FSS superstrate consisting of two-layered FSS screens for dual-band directivity enhancement is introduced as an alternative to an EBG type of dielectric superstrate to reduce its height and facilitate the fabrication process.