4Beam‐Reconfigurable Antennas Using Active Frequency Selective Surfaces

4.1 Introduction

Over the past 20 years, advances in metamaterials have opened up a new era for electromagnetic science and engineering. As a class of artificial structures, metamaterials can be engineered to modify electromagnetic properties that cannot be found in nature. A metamaterial consisting of subwavelength unit cells is essentially a resonant structure, and it is equivalent to a homogeneous material with effective relative permittivity and permeability. Thus, by tailoring these parameters, one can achieve exotic electromagnetic properties such as inversion of the Snell law, inversion of the Doppler effect, backward Cherenkov radiation, etc. Among the metamaterials developed so far, 2D metamaterial structures, usually termed meta‐surfaces, have found many applications in microwave and antenna design because their planar periodic structures can be easily formed by arrays of metallic elements or apertures printed on dielectric substrates. Two typical examples are frequency selective surfaces (FSSs) and electromagnetic bandgap (EBG) structures [1].

2D EBG structure is a variant of the photonic bandgap (PBG) material. Photonic crystals in PBG materials are arranged periodically in high permittivity materials to prevent the propagation of electromagnetic waves in the optical region. To obtain EBG properties in microwave frequencies, 2D planar periodic structures are employed to produce electromagnetic bandstop ...

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