Design of Rectangular Waveguide Bandpass Filters With Transmission Zeros Using High- $Q_u$ Complementary Split-Ring Resonators With Irises

This article introduces a novel bandpass filter designed in rectangular waveguide (RW) technology using an in-line structure. The main design concept involves inserting a complementary split-ring resonator (CSRR) into the RW cross section along with an iris to introduce a transmission zero (TZ) near the passband region. The location of the TZ above or below the passband region is achieved by employing either an inductive or capacitive iris. This structure is modeled as a singlet block, simplifying the design process, as higher order filters can be designed by cascading CSRR-based singlets. Two design methods are presented, each illustrated with a filter example. In addition, the use of tuning screws is also studied. The proposed bandpass filter has been experimentally validated through the fabrication and measurement of a fourth-order prototype designed in the
$C$
-band with TZs at both sides of the passband region. The measurement results demonstrated a high-performance selective bandpass filter with an estimated unloaded quality factor of
$Q_u$

$\approx$
2800.