Pseudoelliptic Combline Filter in a Circularly Shaped Tube

A new configuration of inline combline filter with pseudoelliptic response is presented in this paper. The proposed filter consists of transversally placed and mutually rotated combline resonators inside a cylindrical tube. Various filter configurations with arbitrary placed transmission zeros (TZ) can be obtained by proper resonators arrangement. Furthermore, in comparison to conventional cross-coupled filters, the proposed configuration does not require any additional coupling elements and provides more compact overall dimensions. To validate the proposed configuration a fifth-order filter with two TZ has been designed, manufactured, and measured.