A Substrate-Integrated Evanescent-Mode Waveguide Filter With Nonresonating Node in Low-Temperature Co-Fired Ceramic

A cross-coupled substrate-integrated evanescent-mode waveguide filter is proposed with a quasi-elliptic frequency response. It is realized with a coplanar waveguide as a nonresonating node to provide an equivalent negative coupling coefficient. The filter prototype is developed with folded and ridge substrate-integrated waveguides (SIWs) in low-temperature co-fired ceramic. Since evanescent-mode and cross-coupling techniques are used in the design of filters, about 90% area reduction and more than 60% volume reduction are achieved, in comparison with conventional planar cavity-coupled SIW filters. Their unloaded Q factor is also improved. In particular, the spurious suppression characteristic of the direct-coupled evanescent-mode waveguide filter is kept by the cross-coupled filter with the nonresonating node structure. All these merits are demonstrated numerically, as well as experimentally, with good agreement obtained between the measured and simulated S-parameters.