Synthesis and Design of Substrate Integrated Waveguide Filter Using Predistortion Technique

Substrate Integrated Waveguide (SIW) has been demonstrated for the design of low-cost planar waveguide bandpass filters in the same process as planar circuits. However, SIW cavity resonator generally has a finite Qu of around 500 with most commonly used dielectric substrates, which rounds the passband edge and reduces the effective bandwidth of narrowband filter. In this paper, a K-band bandpass filter with 1 % relative bandwidth and resonators of Qu 500 is synthesized and designed by partial predistortion techniques. The predistorted filter is symmetrically realized by the SIW technology. An effective Qu of about 2500 is obtained and effective bandwidth of the filter is improved. The discrepancy between the actual Qu of SIW cavity resonator and the Qu used by predistortion, as well as the fabrication error lead to the difference between measurement and the simulation results.