A New Approach to Design Differential-Mode Bandpass Filters on SIW Structure

A new approach to design differential-mode (DM) bandpass filters is proposed and implemented based on the substrate integrated waveguide (SIW) technology. By properly constructing the topologies of SIW resonant cavities, the balanced section of the proposed filter achieves an attractive capacity in simultaneously realizing the desired DM transmission and expected common-mode (CM) suppression in a certain band. In design, the specified DM frequency response is achieved with an equivalent two-port circuit model. To illustrate the possibilities of the new approach, a fourth-order Ku-band prototype is designed and fabricated on a single-layer substrate. Measured results agree well with the predicted counterparts.