Development of Substrate-Integrated Waveguide Filters for Low-Cost High-Density RF and Microwave Circuit Integration: Direct-Coupled Cavity Bandpass Filters With Chebyshev Response

Direct-coupled cavity bandpass filters with Chebyshev response are studied and realized, using the technique of planar substrate-integrated waveguide (SIW) for the purpose of high-density integration and cost reduction. Using a general mode-matching technique, the scattering matrix of waveguide bifurcation-type discontinuity and asymmetric iris are established and analyzed. Such discontinuities are used as coupling components and building blocks in the design of filters that are realized on RT/duroid 6002 with the ordinary printed circuit board process in our work. Measurement for one of the three four-pole filters gives 3.4 dB insertion loss and 17 dB return loss over the whole passband at near 24 GHz (K-band) with 440-MHz bandwidth (1.8%). The design method can be widely adopted for the development of microwave-integrated circuits, and the mass-fabrication of such SIW filters can be made easy while maintaining a very low cost.