Analysis of dispersion and series gap discontinuity in shielded suspended striplines with substrate mounting grooves

Dispersion and series gap discontinuity of shielded suspended striplines (SSLs) on Duroid substrate (ε_r=2.22) are analyzed using the finite-difference time-domain method (FD-TD). Numerical accuracy of better than 0.15% is achieved when the FD-TD is used to calculate the effective dielectric constant (ε_reff ) of an air-filled rectangular coaxial transmission line. Data obtained for the frequency-dependent ε_reff of uniform SSLs and both scattering and equivalent circuit parameters of various series gap discontinuities are presented. In general, the presence of sidewall mounting grooves causes a nearly frequency-independent small reduction in ε_reff. On the other hand, proximity effects of the housing are found to be more important. For the gap discontinuity, coupling across the gap is stronger for wider strips and/or narrower gap width. Irregular transmission behavior is also found when the strip is wide enough to interact strongly with the sidewalls