Miniaturized Filters with a Controllable Number of Passbands by Embedding Serpentine Microstrip Resonators in SIW.

This study proposes a novel simple structure based on evanescent‐mode theory for the design of miniaturized filters with good out‐of‐band rejection and controllable passband number characteristics. The filter structure is realized by embedding serpentine microstrip resonators in the upper metal surface of the substrate‐integrated waveguide (SIW). These resonators are composed of upper and lower parts, which form a single‐passband filter when the lengths are equal and a double‐passband filter when the lengths are unequal. This paper proposes a novel method for switching between single‐ and dual‐passband configurations by modifying the length of the serpentine microstrip resonators without altering the overall SIW dimensions. Furthermore, finite transmission zeros are incorporated into the filter to augment the out‐of‐band rejection capability of the filter and the isolation effect between the passbands of the dual‐passband filter. To ascertain the viability of the proposed design, a two‐stage single‐passband filter and a two‐stage dual‐passband filter were fabricated and tested in this study. The experimental results align closely with the simulation outcomes, effectively validating the efficacy of this design. [ABSTRACT FROM AUTHOR]