Compact Wide-Stopband QMSIW-Based BPF for X-Band Applications

A novel and compact two-pole quarter mode substrate integrated waveguide (QMSIW) based bandpass filter with ultra-wide stopband characteristics (rejection level > 20 dB, up to 4.05f₀, where f₀ is the center frequency of the bandpass filter) is designed and developed in this paper. The designed second-order filter comprises of two circular QMSIW cavity resonators. The filter is designed using the dominant TM₀₁₀ mode of the circular SIW cavity. The TM₀₁₀ modes of cavities are coupled through the arc-shaped slot etched in the middle layer. To verify the present design methodology, a second-order bandpass filter is fabricated and its characteristics are measured. The designed bandpass filter shows outstanding performance in terms of good fractional bandwidth of 14.45%, lower insertion loss of 2 dB and wider stopband behavior (rejection better than 20 dB up to 4.05f₀) in a given footprint. The experimental results of the filter matches well the EM-simulated ones.