Abstract
This review paper summarizes various aspects of directive beaming and explains these aspects in terms of leaky waves. Directive beaming occurs in antenna design where a narrow beam is obtainable by using fairly simple planar structures excited by a single source. These structures include Fabry-Pérot cavity structures as well as metamaterial structures made from artificial low-permittivity media. Directive beaming also occurs in the optical area where it has been observed that highly directive beams can be produced from small apertures in a metal film when an appropriate periodic patterning is placed on the film. One aspect that these phenomena all have in common is that they are due to the excitation of one or more weakly attenuated leaky waves, the radiation from which forms the directive beam. This is established in each case by examining the role of the leaky waves in determining the near-field on the aperture of the structure and the far-field radiation pattern of the structure.
Highlights
The subject of directive beaming from planar structures that are excited by a simple source is one that has had a fairly rich and interesting history, extending from the 1950s until the present time
The structure is excited by a simple source inside the substrate, which is shown in Fig. 1 as a horizontal electric dipole in the middle of the substrate, though other sources can be used. This structure has appeared in the literature under various names, including Bcavity reflex antenna,[ BFabry– Perot cavity antenna,[ Belectromagnetic bandgap (EBG) antenna,[ Bplanar leaky-wave antenna,[ and variants of these names. (The term BEBG[ arises from the consideration that the partially reflecting surface (PRS) may consist of a stack of dielectric layers or other elements, forming an EBG structure [14]–[16].) One of the purposes of this paper is to review the general properties of such structures, and to explain how they operate as leaky-wave antennas
The subject of directive beaming from planar structures at microwave and optical frequencies has been reviewed, with the aim of explaining how the various phenomena are due to the excitation of one or more leaky modes on the structure
Summary
Directive beaming through periodic structures at microwave and optical frequencies are discussed in this paper, as is the role of weakly-attenuated leaky waves in these structures. This is established in each case by examining the role of the leaky waves in determining the near-field on the aperture of the structure and the far-field radiation pattern of the structure. KEYWORDS | Directive beaming; electromagnetic bandgap (EBG) antenna; enhanced transmission; Fabry–Perot cavity; leaky-wave antenna; metamaterial; plasmon
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