The Effect of the Parallel-Plate Mode on Striplines in Inhomogeneous Dielectric Media

Striplines are widely used in high speed printed circuit boards (PCB). When the stripline is in inhomogeneous dielectric media, its principle operation mode is quasi-TEM. In this case, the parallel-plate mode between two ground planes can be excited as a parasitic mode. This paper investigates the effect of this parasitic mode on striplines through simulations. The simulated S-parameters of striplines when this parallel-plate mode is excited and suppressed are compared. The measured S-parameters of striplines with and without the ground stitching vias are also compared. The impact of the parasitic mode on time domain crosstalk and eye diagram is also shown.