WR-2.8 Band Pseudoelliptic Waveguide Filter Based on Singlet and Extracted Pole Resonator

In this paper, a novel WR-2.8 band (260-400 GHz) pseudo-elliptic waveguide bandpass filter (BPF) based on a singlet and an extracted pole resonator is proposed. The singlet based on TE301 mode and extracted pole resonant cavities is developed to generate two transmission zeros (TZs) on both sides of the passband in order to achieve high selectivity. The mechanism of TZs generation of both structures is analyzed in this paper, and TZs position is predicted precisely. Furthermore, each TZ position can be controlled independently by changing the dimensions of resonant cavities. The proposed filter fabricated by conventional computer numerical control (CNC) milling technology exhibits an insertion loss (IL) around 0.7dB, a 3-dB fractional bandwidth (FBW) of 9.9% centered at 357GHz and an ultra-high selectivity with a 0.87 30-dB rectangular factor which is all in good agreement with the simulations. To the best of the author's knowledge, 0.87 is the highest 30-dB rectangular factor among such wide fractional bandwidth THz BPF in the open literature. This high-performance filter is capable of improving the sideband rejection receiver performance.