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 novel $H$ -plane waveguide in-phase power divider (also known as combiner) with high isolation working across full WR-3 band (220-330 GHz) is realized in this paper. This distinctive architecture is designed based on the sum-difference principle of Magic-T, whose $E$ -plane branch (difference port) is matched with an $E$ -plane T-junction. Both effects of processing and assembling uncertainties on this power divider/combiner performance are discussed in detail to display error sensitivity. The physical prototype is split into three blocks and processed by the state-of-the-art computer numerical control (CNC) milling technology. The absorbing materials are housed in the loaded T-junction arms to terminate return wave as well. Compared with the most reported terahertz waveguide power couplers, the meaningful measured results of this advanced in-phase power divider are delivered. The input and output matching as well as high isolation have been obtained over full WR-3 band, when an 11 dB reference level is considered. A total insertion loss of about 1.2 dB is achieved including three straight waveguides having a total length of 30 mm, which is also in good agreement with simulations. This module, which is fully compatible with the standard CNC-milling technique, can be directly integrated to terahertz detection systems.

Filters play an invaluable role in most detection and communication systems, blocking unwanted, harmonic or mirrored waves. In this paper, two $3^{\mathrm {rd}}$ -order quasi-elliptical waveguide bandpass filters working at 400 GHz are developed based on TE ₁₀₂ -mode oversized resonators. Transmission zeros are generated through the physical cross-couplings and the mixed modal bypass couplings. $H$ -plane off-axis coupling structures without any fragile irises are adopted to strengthen robustness and simplify manufacturing at such high terahertz frequencies. Effects of processing uncertainties on filters performance are discussed in detail to display error sensitivity. Two computer numerical control (CNC) machined filters exhibit a minimum insertion loss of about 1.5 dB in a 3 dB fractional bandwidth (FBW) with 12% centered at 390 GHz @ Filter-I, and 9% FBW with a center frequency of 394 GHz @ Filter-II, which are all mainly agreement with simulations. The performance is highlighted with the reported terahertz filters, which indicates that both architectural designs are still suited for the delicate CNC-milling restriction in such high WR-2.2 band.

A wideband multi-polarized square-horn antenna based on an orthogonal mode transducer (OMT) is developed for working in the whole W-band in this paper. The designed antenna is capable of radiating multiple polarization modes as horizontal polarization (HP) and vertical polarization (VP) when as single-port excitation and left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) when as dual-port excitation, owing to the characteristic of the OMT with the transmitting of orthogonally polarized waves. A CNC-layered fabrication approach is proposed, which means that the antenna prototype integrating with a Boifot-type OMT, turning waveguide, twisting waveguide and phase shifter is divided into three layers along the vertical direction to be fabricated based on computerized numerical control (CNC) technology. In the design, the turning waveguide and twisting waveguide are employed to achieve plane consistency of the antenna branch ports. Furthermore, a phase shifter is designed to compensate the orthogonally polarized waves, which can keep the phase of the orthogonally polarized waves consistent in a wideband frequency range from 75 GHz to 110 GHz. A prototype is fabricated and measured to verify the performance of the proposed multi-polarization antenna, and the measured results agree well with the simulation ones. In the whole W-band, the value of return loss is better than 10 dB of all polarization modes, and the value of AR of the LHCP and RHCP is below 3.5 dB. The maximum gain of the antenna reaches up to 18.8 dBi at 110 GHz. In addition, regarding the layered structure, the possible layered assembly error analysis is discussed, which verifies the feasibility of the layered machining for this antenna.

A conformal circularly polarized H-plane horn antenna with broadband and low-profile characteristics is proposed in this paper, which is integrated with quasi-Yagi and wrapped around a hollow cylinder. The H-plane horn based on bent corrugated substrate integrated waveguide (BCSIW) technology and the quasi-Yagi with fan-shaped driving elements provide the vertical and horizontal linear polarized waves respectively, which generates circularly polarized radiation combining with the suitable phase delay provided by the transition section. The proposed antenna is wrapped around a hollow metallic cylinder with radius of 100 mm and height of 90 mm. The measured voltage standing wave ratio (VSWR) of the fabricated antenna is less than 2.0 in the frequency range over 9.4 GHz (81%) while the axial ratio (AR) is below 3 dB from 9.4 GHz to 21.7 GHz (78%). The antenna also exhibits stable radiation pattern with peak gain of 12.1 dBi and a cross-polarization below -17dB over the whole frequency range. It is observed that the measured results agree well with simulated ones.