A 220-GHz low-loss and wideband waveguide bandpass filter with fourth-order quasi-elliptic response is presented and analyzed in this letter. An electric cross-coupling realized by easily manufactured capacitive iris is introduced in the classical folded quadruplet topology. The prototype fabricated by conventional computer numerical control (CNC)-metal-milling technology exhibits meaningful results of an insertion loss of around 0.6 dB and a 3-dB fractional bandwidth of 9.8% centered at 214.3 GHz, which are in excellent agreement with the simulated ones. The effects of tolerance and surface roughness on the filter performance are discussed in detail. All the results indicate that the present CNC process can meet the accuracy and roughness requirement of such waveguide filter in WR-4 band.

A W-band dual-band waveguide bandpass filter with each passband of fourth-order quasi-elliptic response and flexibly allocated frequency and bandwidth ratios is presented by adopting an advanced coupling scheme and introducing easily manufactured electric coupling structures. An experimental prototype centered at 80 and 100 GHz is fabricated by the computer numerical control (CNC) milling technology, and an excellent agreement is achieved between the measurements and simulations. The effects of machining tolerances and surface roughness on filter performance are also discussed, indicating the conventional CNC process can completely meet the accuracy and roughness requirements of such W-band dual-band waveguide filter.

Modern terahertz (THz) receivers used in radio astronomy are aimed at developing multi-pixel instruments, in which polarization twists are often required. In this paper, an all-in-one and low-loss 90° waveguide twist is developed for working over the full WR-3 band. A square waveguide junction with doubler-corner-cut is integrated between the H-plane and E-plane waveguides to provide 90° polarization rotating. All the vertical corners are fillet to comply with the fabrication constraints of the current computer numerical control (CNC) machining. The prototype integrated with a twist section of 1/4 wavelength thickness and two straight waveguides with total 12 mm length is processed through means of split-block. Measured results exhibit a low insertion loss of 0.4 dB and better than 25 dB return loss across the entire WR-3 band, which are all in good agreement with simulations. Such excellent performance is highlighted comparing with the reported THz waveguide twists, which indicates that this compact design is well suited for delicate CNC-machining restrictions in THz band.

A high‐performance waveguide bandpass filter operating at W ‐band is presented. This folded fourth‐order filter with quasi‐elliptic response is developed by introducing cross‐coupling and source–load coupling, while maintaining a compact construction for simple computer numerical control (CNC) milling process. The filter fabricated within aluminium block shows an insertion loss of about 1.2 dB in a 3 dB fractional bandwidth of 5.5% from 90.1 to 95.2 GHz, which are very close to the simulated results in the full W ‐band.

On-chip filters play an invaluable role in most detectors and instruments, blocking unwanted, harmonic, or mirrored signals. In this article, two coplanar waveguide bandpass filters working at 350 GHz are designed based on quarter-wavelength stepped impedance resonators, which can be easily integrated in on-chip systems. A second-order filter with a classical Chebyshev response and a fourth-order filter with quasi-elliptical characteristic is developed together to define the roll-off performance. Both filters are patterned based on superconducting niobium film by the optical lithography and lift-off process, which could reduce the significant metallic loss in high terahertz band. All the chips integrated with transitions are evaluated through a quasi-optical system, which is built based on the sensitive superconductor-insulator-superconductor tunnel junction detector at cryogenic temperature. The calibrated transmission responses, which are matched with simulations, have indicated that such superconducting coplanar waveguide filters can be enabled in future terahertz astronomical spectrometer.