Radiation analysis in the space domain of laterally shielded planar transmission lines

The propagation and radiation characteristics of leaky-wave modes in laterally-shielded planar waveguides are studied by a novel approach based on space domain parallel plate waveguide (PPW) mode expansion. This method introduces the discrete PPW propagation and radiation spectra for each leaky-wave mode, and allows a direct interpretation of the radiation phenomena by a superposition of modal PPW radiated fields. Each PPW mode farfield radiated pattern is created by a continuous spectrum of cylindrical inhomogeneous waves. However, some interesting features, such as the maximum radiation direction or the total-reflection phenomena for nonradiative PPW modes, can be approximated using plane-wave refraction theory for each non-uniform PPW plane-wave. With this theory, the discrete PPW radiation spectrum can be related directly to the continuous radiation spectrum of this type of open waveguide leaky-mode, in an attempt to unify the theory of guiding and radiation phenomena. Results are obtained for a laterally-shielded top-open suspended microstrip waveguide, but this method is extensible to any laterally-shielded multilayered and multiconductor open waveguide.