Quasi-TEM waveguides realized by FSS-walls

Recently, great interest has been devoted to the realization of artificial magnetic conductors (AMC) through the use of periodic surfaces. This kind of structure can be used in several practical applications. An interesting application of AMC surfaces is concerned with the possibility of realizing quasi-TEM waveguides, characterized by a uniform field distribution and by a phase velocity equal to the speed of light. A quasi-TEM waveguide implementation based on printed FSS on two walls of a rectangular waveguide has been proposed (Fei-Ran Yang et al., IEEE Trans. Microwave Theory and Techniques, vol.47, no.11, 1999). At the resonance frequency of the FSS, the side walls act as magnetic walls, thus supporting the propagation of quasi-TEM mode. Using a "hard" boundary condition on the wall imposes annulment of both the E and H components along the direction of propagation; thus the hard surface is well suited for supporting a quasi-TEM propagation inside waveguides. A hard surface can be realized by printing dipoles on a thin grounded dielectric slab. We use this solution for loading walls in both rectangular and circular waveguides to obtain quasi-TEM waveguides. The design process is described. The results are compared with those from an independent code.