Sub-THz Waveguide Band-Pass Filter: Design, Analysis and Fabrication Repeatability

This paper presents two units of Y-band (325-500 GHz) and two units of D-band (110-170 GHz) all-pole inline Chebyshev band-pass filters (BPFs) using high-precision computer numerically controlled milling. The filters are based on six-coupled resonant cavities and are designed for a 20 dB return loss in a 10 GHz bandwidth centered around 470 GHz and 160 GHz with two taper sections at the input and output. Statistical analyses of the design parameters are performed to estimate the manufacturing tolerance. Microscope measurements are done and it is seen that machine tolerance on cavity lengths of about 3.5 microns causes a 2 GHz center frequency shift in Y-band. Measurements validate the analyses. The fabrication repeatability in the D-band is more consistent than in the Y-band. Indeed, two Y-band BPF units have a center frequency shift difference of 6 GHz while the the D-band BPF units have almost identical responses.