Microwave and Terahertz Antennas and Circuits

Abstract

As has been mentioned already, the idea of achieving a control of the dielectric permittivity in the microwave region through the use of one, two or three-dimensional periodical ensembles of metallic elements is far from being a novelty. Already during the 1960s, the propagation of waves in two-dimensional periodical structures or in three-dimensional stacks of spheres had started being investigated, using at this time the concept of an artificial dielectric (Harvey 1959). However, the new interest for periodical structures in the field of microwaves has largely extended beyond these limits. First, it is quite apparent that microwave devices, which often can be more easily realized than their optical equivalents, have permitted the validation and the simpler demonstration of a series of new effects related to photonic crystals (Danglot 1998; Gadot 1997; Lourtioz 1999; Özbay 1996; Pendry 1996; Shelby 2001; Sievenpiper 1996, 1998, 1999a; Smith 2000b; Yablonovitch 1991a, 1991b). In the microwave region itself, the detailed study of three-dimensional structures, the analysis of periodicity defects, the combination of photonic crystals with active devices, the increase in frequencies well beyond the gigahertz, and more generally the development of modelization and characterization methods, were still in their infancy at the time of artificial dielectrics. Finally, from a practical point of view, the combination of photonic crystals with microwave circuits and antennas has led to envisioning the possibility of several important applications, even if it is too early, in view of the great variety of currently existing microwave techniques, to assess their actual potentialities.