Stopband Performance Improvement of CSRR-Loaded Waveguide Bandpass Filters Using Asymmetric Slot Structures

This letter presents a simple waveguide filter structure having planar structure that can control transmission zeros (TZs) and center frequency independently. The planar structure is composed of the conventional complementary split-ring resonator (CSRR) and asymmetric slot structures. The planar structures resonate at particular frequencies and introduce total 2N TZs, above and below the passband of an Nth-order filter, and thus also improve the stopband performance of a planar CSRR-based waveguide bandpass filter. To demonstrate it, a third-order CSRR-loaded bandpass filter has been considered and analyzed. It has been shown that by varying the length of the asymmetric slot structures the TZs can be independently controlled.