Practical Design and Implementation Method for Asymmetric-Response Post-Loaded Substrate-Integrated Waveguide Filters

This paper presents a practical method for implementing a post-loaded substrate-integrated waveguide (SIW) filter producing an asymmetric response with a pair of near-band transmission zeros. More specifically, we present a practical frequency-dependent coupling structure for post-loaded SIW resonators for implementing an asymmetric response. By virtue of the proposed coupling design methods, the roll-offs in the upper and lower stopbands can be readily controlled to be different from each other. In other words, the roll-off in a stopband can be made to be steeper than the one in the other stopband by means of using the proposed design method for coupling structure. More importantly, we propose a useful approach to swap the two stopband responses of an asymmetric-response filter. In other word, this paper shows a practical method to laterally reverse an asymmetric response. For demonstration, 1 symmetric-response and 2 asymmetric-response fourth-order SIW filters have been designed using the presented frequency-dependent coupling structures.