A new differential line based on a periodic microstrip-CPW hybrid structure

A new differential periodic transmission line with broad common-mode suppression is presented. The unit cell consists of a hybrid microstrip-coplanar waveguide structure involving two symmetrical edge-coupled microstrip lines coupled to a coplanar waveguide resonator etched in the ground plane. Transmission-line models have been used to analyze the structure response in both the differential and common modes. The device exhibits all-pass characteristics under differential-mode operation and a bandstop response for the common-mode signal. A Bloch-Floquet analysis allows for the prediction of the required common-mode rejection band. Good agreement has been found between measurements, electromagnetic simulations and analytical results.