Substrate integrated waveguide highpass filter with high selectivity

A novel substrate integrated waveguide (SIW) highpass filter with sharp attenuation characteristics using shunt SIW resonant stubs is proposed. The highpass filter consists of a main SIW transmission line loaded with three shunt SIW resonant stubs. The three shunt SIW resonant stubs are used to realise the band-stop filter, whose stopband is designed to coincide with the transition band of the SIW highpass filter. Therefore, the sharp attenuation of the stopband filter contributes to the attenuation of the entire filter. To verify the concept, a filter prototype with a cutoff frequency of 16 GHz is designed, fabricated and measured. Another hybrid filter with the same specifications is fabricated and compared. The measured results show that the proposed filter has sharper attenuation characteristics than the hybrid filter.