110–170 GHz Bandpass Filter with Steep Rejection Slope Based on Symmetrical H-plane Cavities

Le résumé fourni par la source

A 110–170 GHz bandpass filter (BPF) is presented with sharp roll-off slope in the stopband. To improve the suppression level in the stopband at unwanted frequencies close to the passband, a symmetrical type of H-plane cavity is designed and applied to the filter. The symmetrical H-plane cavities (SHC) are H-plane symmetrical step extensions on the fundamental-mode rectangular waveguide. It increases the reliability and simplicity without complicating the filter structure. The prototype BPF is implemented based on the waveguide H-plane-iris structure combined with two SHCs. The required passband from 110 GHz to 170 GHz is obtained by the H-plane-iris structure. The two SHCs are designed to resonate at 179 GHz and 181 GHz, respectively, for the desired out-of-band suppression level. The BPF cavity is divided into two E-plane split-block halves for the all-metal fabrication. The precision CNC milling process is employed with the gold-plated brass. The accuracy is better than 5 µm and the surface roughness better than 0.4 µm. The whole dimension of the prototype BPF is 30 mm × 20 mm × 20 mm. The measured results show the insertion loss of typically 1.2 dB over 106–174 GHz frequency range. The measured center frequency shifts downwards by no more than 1.2 GHz compared to the simulations. The suppression level is greatly improved from 8 dB to better than 30 dB at 178 GHz, without disturbing the passband performance. The reliability and simplicity are increased taking advantage of the simple fabrication process and the symmetrical structure, which minimize the frequency offset and are suitable for volume production.

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