Compact inline substrate integrated waveguide filter with enhanced selectivity using new non-resonating node

A high selective inline substrate integrated waveguide (SIW) filter based on novel stepped-impedance non-resonating node (NRN) is presented. The stepped-impedance NRN is realised by inserting a stepped-impedance substrate integrated coaxial line resonator into the volume of a third-order SIW filter. It introduces extra signal transmission path between source and load. Thus, one more transmission zero (TZ) is produced compared with conventional NRN that further improves the selectivity of the filter. Also, the proposed filter achieves a compact circuit size as the stepped-impedance NRN is embedded in the SIW cavity without occupying extra layout. To validate the proposed concept, a prototype filter with two TZs locating at both the lower and upper stop-bands, is designed, fabricated and measured. The measured results are well consistent with the simulation ones.