Complex waveguide filter topologies employing inductive windows and dielectric objects

This study presents novel topologies for implementing bandpass elliptic filters employing waveguide structures composed of inductive windows and dielectric objects. Cavities operating in dual mode are obtained by placing a dielectric post inside a cavity. By combining dual mode with single mode cavities, several useful filter responses implementing transmission zeros can be synthesised. The first proposed structure is a three-pole filter with one transmission zero, using a physically asymmetric configuration with two waveguide cavities and one dielectric post. The second proposed structure implements a four-pole filter with one transmission zero, employing a physically symmetric configuration with one dielectric post and three waveguide cavities. The third structure implements two transmission zeros in a four-pole filter, also employing a symmetric structure, but now with two dielectric posts and two cavities. Important aspects on sensitivity issues of the new structures, as well as on synthesis techniques, needed to obtain the required topologies, are introduced. This includes several alternatives to implement a transfer function, using physically symmetric or asymmetric structures. Finally, a transversal filter with one dual-mode cavity using a dielectric post has been manufactured and tested with good results. This is the first time that this type of filters is experimentally demonstrated.