Yun Zhao

The development of next-generation terahertz (THz) transmitters and receivers based on 3D stacked packaging technology relies heavily on the integration of high-performance waveguide directional couplers. This paper presents an accurate and efficient method based on the mode-matching method (MMM) for the rapid analysis of a branch waveguide coupler fabricated through a silicon-based 3D stacking process. In contrast to the traditional method using the finite-element method (FEM) in HFSS, which is cumbersome and time-consuming, the proposed method offers orders-of-magnitude speed improvement. It is especially well-suited for large-scale uncertainty error analysis and statistical evaluation of THz waveguide couplers and related components. This theoretical MMM is validated through an experiment by characterizing a deep reactive ion etching (DRIE) fabricated and 3D stacked 220 GHz waveguide coupler.

This paper presents a high gain, broadband silicon micromachined diagonal horn array antenna for the 190 GHz to 250 GHz frequency band. The antenna array is configured to be built from 34 silicon layers. The upper 25 layers of silicon wafers create an 8×8 diagonal horn array antenna and the lower 9 layers form the feed network. The diagonal horn is selected as a radiation element for its 45° polarization direction, which suppresses side and grating lobes in the E-plane and H-plane after array formation. Polarization converters are innovatively employed in the feed network to resolve the issue of opposite polarization from waveguide T-junctions. In order to meet the silicon micromachining criteria, all diagonal horns and the feed network are step-profiled designed based on silicon wafer thickness. The 34 silicon layers are aligned and fixed by CNC-milling metal tooling. Monte Carlo analysis is utilized to quantify the interlayer offset errors introduced during the assembly of the wafers. The measurement results are within the error allowance. The antenna achieves a peak gain of 30.9 dBi and a working frequency bandwidth of 27%. Characterized by highly directive radiation patterns with low side lobe levels in the E-plane and H-plane, the antenna is well-suited for next-generation THz point-to-point communication systems.

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.

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.

This paper presents a waveguide–slot antenna to generate a radiation beam with high gain fed by a low-loss feeding network at 110 GHz. The proposed antenna consists of a compact eight-way power divider and a waveguide–slot array. The eight-way power divider provides equal-amplitude and alternative-phase excitation for the slot array, and each of them supports two waveguides. The integral structure is implemented by two layers with a channeled substratum and a slotted superstratum. To verify the proposed slot array, the designed array is fabricated with computer numerical control (CNC) milling and measured. The measured peak gain of the designed antenna is 32 dBi at 110 GHz. The proposed antenna with a simple structure provides a promising solution to develop high gain antenna in upper millimeter-wave and sub-terahertz (THz) applications.

Terahertz (THz) band, which owns abundant and underexplored frequency spectrum, has provided rich scientific and technological opportunities in numerous research fields, such as radio astronomy, atmospheric science and high‐speed communication. As one of the key components in THz systems, the multiplexer cannot only separate/combine different bands, but can also promote the development of THz instruments toward wider band and more multibands. Thanks to the high‐precision computer numerical control milling and micromachining technologies, a lot of THz waveguide multiplexers have been reported in recent years. According to the classification of design configurations, this article offers a brief overview on the developed THz multiplexers. In addition, the performance and system applications of different waveguide‐typed multiplexers are discussed. Therefore, this review will provide a valuable reference for the further development of THz waveguide multiplexers with high performance.

A W-band H-plane horn array antenna with tilted radiation beam based on waveguide structure is proposed in this paper. The designed antenna array consists of four H-plane antenna elements and a broadband feed network. The distribution of excitations is determined by the theory of maximum power transmission efficiency (MMPTE). A multiple branch coupler, two T-junctions and three fixed phase shifters are employed to construct the feed network, which can generate the required amplitude and phase in broadband frequency range from 80 GHz to 100 GHz. The computer numerical control (CNC) milling machines technology is employed to machine the feed network and antenna. All measured and simulated results are in good agreement, which verify the feasibility of the theory of MMPTE to generate a radiation beam directed to any angle from −35° to 35° with suitable excitation provided by the proposed feed network in this paper.

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 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.

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.