Temporal and Spatial Dispersion Engineering Using Metamaterial Concepts and Structures
Shulabh Gupta,a Mohamed Ahmed Salem,b and Christophe Calozb,c
aDepartment of Electronics, Carleton University, Ottawa, Ontario, Canada
bPoly-Grames, Polytechnique de Montreal, Montreal, Canada
cElectrical and Computer Engineering Department, King Abdulaziz University,
Jeddah, Saudi Arabia
Electromagnetic metamaterials (MTMs) are broadly defined as artificial effectively homogeneous electromagnetic structures with exotic properties not readily available in nature. They consist of an arrangement of subwavelength scattering particles emulating the atoms or molecules of real materials with enhanced properties. The scattering particles are typically arranged in a periodic lattice with the unit cell size p ^ 1g, where 1g is the guided wavelength inside the MTM. Under such operating conditions, the structure behaves as
Broadband Metamaterials in Electromagnetics: Technology and Applications Edited by Douglas H. Werner
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ISBN 978-981-4745-68-0 (Hardcover), 978-1-315-36443-8 (eBook) www.panstanford.com a real material so that the electromagnetic waves sense the average, or effective, macroscopic and well-defined constitutive parameters, which depend on the nature of the unit cell. Their 2D counterparts are known as metasurfaces, which are thin layers of subwavelength resonant scatters that interact strongly with electromagnetic waves for achieving unique wavefront processing functionalities.
One of the classical functionalities of MTMs is negative refraction, which requires simultaneous occurrence of negative e and m within the desired frequency range. However, it is physically impossible to achieve negative e and m in a non-dispersive medium to satisfy energy conditions, and thus metamaterials are inherently dispersive with frequency-dependent material parameters [e(w) and mi.®)] to exhibit such exotic effects [Caloz and Itoh (2006)].
The first MTM implementations were dominantly volumetric arrangements ofresonant particles consisting of split-ring resonators and wired mediums to realize effective e(a> and m(w) for achieving negative refraction. However, the resonant nature of the particles gave them narrowband and lossy characteristics. Later, Caloz and Itoh (2006) developed the concept of composite right/left-handed (CRLH) transmission lines, which act as a left-handed transmissions line at low frequencies and right-handed transmissions line at high frequencies. They were based on tightly coupled particles, which resulted in broadband planar structures with low losses.
The rich electromagnetic characteristics of metamaterial CRLH lines combined with their broadband nature recently led to the novel paradigm of radio-analog signal processing (R-ASP) for processing broadband signals using exotic and unique dispersion functionalities of such MTMs, metasurfaces, and MTM-inspired structures [Gupta and Caloz (2009); Caloz (2009)]. This chapter focuses on this aspect of MTMs and develops a conceptual foundation for a unique class of R-ASP systems: real-time spectrum analyzers (RTSAs).
The chapter is organized as follows. Section 5.2 introduces R-ASP and its core signal processing component called phaser. These phasers are typically of two types, temporal and spatial, and the spatial types are expanded upon in Section 5.3 for real-time spectrum analysis applications. This section discusses two commonly used spatial phasers: a diffraction grating and leaky-wave antenna (LWA), with a detailed description of metamaterial LWAs as a practical device to be used in the rest of the chapter. Once the phaser components are presented and explained, Section 5.4 presents 1D/2D RTSAs using LWAs and discusses their typical system features and characteristics. Finally, a metasurface phaser-based spatial 2D RTSA is presented in Section 5.5.