Analysis and application of metamaterial spiral-based transmission lines

Double spiral resonators, properly backed on grounded substrates and specifically arranged in periodic arrays, support backward waves at their fundamental resonance. Transmission lines that are composed of these spirals and their potential use in microwave applications are studied in this paper. Subsequently to a periodic, full-wave analysis of the double spiral resonators, the fabrication and measurement of the spiral-based transmission lines experimentally validate that they support backward waves over a fractional bandwidth of approximately 13%. For the in depth analysis of these lines, an equivalent circuit, that can describe all the phenomena associated with the operation of the double spirals as structural unit cells of metamaterials, is extracted. Finally, an ultra compact diplexer that originates its operation on spiral-based transmission lines is presented, exhibiting just one of the possible ways that metamaterial lines can be employed in microwave applications.