A Dual-Band Bandpass Filter Based on Hybrid Structure of Substrate Integrated Waveguide and Substrate Integrated Coaxial Line

This paper presents a novel dual-band bandpass filter design based on hybrid structure of substrate integrated waveguide (SIW) and substrate integrated coaxial line (SICL), which is implemented by multi-layer printed circuit board process. The hybrid structure is realized by inserting the SICL resonator into the volume of the SIW cavity which enables the hybrid structure to support the co-transmission of two orthogonal transmission modes (TE10 in SIW and TEM in SICL). Exploiting the two transmission modes, filter with dual-band transmission characteristic can be realized with the upper frequency band determined by the coupled SIW cavity resonators and the lower frequency band controlled through the SICL resonators. Therefore, it brings great flexibility to design dual-band filters as the two passbands can be independently designed. In order to validate the proposed concept, a prototype for Ka-band local multipoint distribution service (LMDS) application is designed, fabricated and measured. Good agreements can be observed between the simulation and the measurement.