STUDY OF LEAKAGE IN MICROSTRIP LINES WITH SEMIINFINITE SUPERSTRATE

The present work is devoted to the 2-D study of microstrip lines with an upper dielectric semiinfinite layer. The final goal is to characterize the evolution of the modal spectrum of these structures as the upper halfspace permittivity (eu) varies. Thus, the evolution of proper and improper modal solutions as eu increases from its lower possible value (e0) to values higher than the microstrip substrate permittivity (e) is analyzed. Due to physical reasons, it is expected that only space-wave leaky modes (SPWLM) are present for eu >e . This assumption is corroborated by the obtained numerical results. In addition, the computed results also show a new kind of physical modal transition from the fundamental bound mode to a physically-meaningful SPWLM.