A Compact W-Band Waveguide Lowpass Filter With Sharp Cutoff Skirt and Wide Stopband

In this letter, a low-loss W-band waveguide lowpass filter (LPF) is proposed with improved frequency selectivity, wide stopband, and compact size. The novel design is capable of achieving a sharp cutoff skirt by introducing transmission zeros (TZs), which are obtained by exciting the TM<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> mode. The bandwidth and TZ’s positions can be controlled flexibly through adjusting the size of resonators and the offset of coupling slots, respectively. Moreover, by controlling the frequency of higher order modes, namely, the harmonic staggered technique, a wide spurious-free frequency response is realized. For demonstration, the proposed W-band LPF is fabricated by computer numerical control (CNC) milling technology, and the measured results show the lowest insertion loss is 0.25 dB, and the 50-dB stopband rejection is achieved from 92 to 210 GHz.