Quasi-elliptic function doublet filters without cross coupling

This paper presents a recent investigation of miniature microstrip doublet dual-mode filters that exhibit quasi-elliptic function response without using any cross coupling. It shows that a single two-pole filter or the doublet can produce two transmission zeros resulting from a double behavior of the dual-mode resonator of this type. Electromagnetic (EM) simulation and experiment results are described. A four-pole filter of this type is demonstrated.