EBG Common-Mode Filter Design Using Uncoupled Coplanar Waveguide to Microstrip Transitions

This letter investigates the effects of an Electromagnetic Bandgap (EBG) common-mode filter design using coplanar waveguide (CPW) to microstrip transitions on differential signals. Specifically, the improvements in the frequency and time domains are studied by s-parameters and eye diagrams. EBG structures are based on a periodic alteration of even-mode impedances to create stop bands in the common-mode, while not affecting the differential mode as much as possible. The proposed common-mode filter is unique in the way that a broad bandwidth is achieved by choosing one of the even-mode characteristic impedances as small as possible. This EBG structure is implemented on a printed circuit board (PCB) and characterized using a 4-port vector network analyzer (VNA).