Metamaterial claddings for waveguide miniaturization

Summary form only given. The study of waveguides loaded with metamaterials has become quite popular in recent years (R. Marques et al., PRL, 89-18, 183901, 2002, S. Hrabar et al., IEEE Trans. Antennas Propag., vol. 53, no. 1, pp.110-119, 2005). It was pointed out that a rectangular waveguide below cut-off behaves as a 1-dimensional electric plasma for TE modes (R. Marques et al., PRL, 89-18, 183901, 2002). Likewise it behaves as magnetic plasma for TM modes (J. Esteban et al., IEEE Trans. on Microwave Theory and Techniques, vol. 53, no. 4, 2005). Since the rectangular waveguide naturally provides negative permittivity below cut-off, when combined with negative permeability materials, such loaded waveguide mimics the double negative materials in the frequency range where the negative permeability and permittivity overlaps. Backward waves in such waveguide were also experimentally verified. It is also of interest to investigate what happens when the waveguide is loaded with negative permittivity medium. It turns out that negative permittivity medium provides a pass band below cut-off inside the negative permittivity region (Y. Dong and T. Itoh, IEEE Microwave Magazine, 2012). The waves in such waveguide are forward waves unlike the former.