Waveguide bandpass filter with multiple transmission zeros

This paper presents a lightweight waveguide bandpass filter using planar structure insert, which can control the location of transmission zero and center frequency independently. The proposed planar insert consists of three concentric circular complementary split-ring resonators. The structure resonates at a particular frequency and produces two transmission zeros above and below the passband, thus improving the stopband performance of conventional complementary split-ring resonator-loaded waveguide bandpass filter. To demonstrate this, a second-order bandpass filter has been designed. It has been shown that by varying the split gap dimensions of upper and lower circular complementary split-ring resonators, the transmission zeros can be independently controlled.