Compact Millimeter-Wave Wideband Bandpass Filter Design Using Triple-Mode Rectangular Ridge Resonator

A novel rectangular air-filled cavity with three parallel ridges is proposed to realize a triple-mode resonator. The resonant frequencies of the first excited triple mode (TE101, TE102, and TE103 modes) are much lower than those of a normal rectangular resonator. Therefore, the triple mode of the resonator can be used to achieve a wideband bandpass filter (BPF) with compact size and low insertion loss (IL). The bandwidth can be tuned by changing the parameters of the ridges. Furthermore, two resonators can be cascaded to obtain a sixth-order BPF for improving the selectivity characteristics. A triple-mode BPF with center frequency (CF) of 92.5 GHz and 3-dB fractional bandwidth (FBW) of 26.9% is designed. Meanwhile, a six-order BPF with CF of CF of 92.8 GHz and 3-dB FBW of 31.7% is presented. The two BPFs are manufactured to show size compactness with good performances, of which the measured IL is 0.2 dB.