Physical and Technological Aspects of Microstrip EBG Filter Design

Some physical and technological aspects of the electromagnetic bandgap (EBG) common-mode (CM) filters are discussed. A simple EBG notch filter for CM in edge-coupled differential microstrip pair is designed using full-wave numerical electromagnetic software. Mixed-mode S-parameters of the EBG structure are analyzed as functions of its basic geometry, including size and number of EBG patches, gaps between them, geometry and position of signal traces across the EBG patches. In this work, one and two differential pairs crossing the EBG patches are considered. It is shown that the filter performance depends on various technological features, such as frequency-dispersive core and prepreg on a PCB; trapezoid shape of signal traces; conductor surface roughness on signal traces and return planes, including EBG patches; length imbalance on the differential pair; and rate of coupling of lines within each differential pair and between the pairs. A number of EBG filters with some geometrical variations, all operating at the frequency of 19.2 GHz, were designed and tested. The measured data validates the modeling results.