High Selectivity Filters in Coaxial SIW Based on Singlets and Doublets

The implementation of singlets and doublets in coaxial SIW technology is presented in this paper. The proposed structures are based on the introduction of a direct source/load bypass coupling using end-coupled embedded coplanar lines. The modelling and design of these structures are discussed, and then two prototypes are designed, manufactured and measured, thus showing the validity of the proposed approach and its potential application for implementing highly selective responses in a very compact footprint.