Peter G. Huggard

The design, fabrication, and performance of a millimeter-wave waveguide orthomode transducer (OMT) operating over an extended W-band frequency range 70–116 GHz is presented. The OMT has been designed for integration within a cryogenic radio astronomy focal plane array millimeter-wave receiver. In addition to delivering necessary millimeter-wave performance, a custom mechanical housing incorporating suitable waveguide interfaces is required. Within the OMT, a turnstile junction performs polarization separation of a signal entering a bespoke circular waveguide interface into two orthogonally polarized outputs via WR10 standard waveguide flanges. The device’s internal architecture was optimized using a combination of proprietary software and a commercially available 3-dimensional electromagnetic field analysis package. In order to demonstrate required performance, compactness and reliable production, two approaches were taken with respect to device mechanical fabrication: platelet and split block direct machining methods. Both structures were manufactured and tested at room temperature. Due to advantages in machining and assembly, the split block concept was selected for inclusion with the array receiver.

The development of terahertz (THz) technology exploiting untapped bandwidth is essential for sensing and communications in 6G and beyond. Instrumentation systems for evaluating the performances of THz devices are of increasing interest. Currently, THz device testing with electronics-based vector network analyzers (VNAs) requires a series of frequency extender pairs to cover all individual bands in the THz range. This increases system complexity and cost. Here, we report on an ultrawideband (UWB) photonic THz source, which will enable simpler and cost-effective THz device testing. The source employs a modified unitraveling-carrier photodiode (MUTC-PD) operating from 100 to 600 GHz. The InP-based MUTC-PD is hybrid-integrated with a UWB high-resistivity Si waveguide interface to efficiently couple the optically generated THz waves to the device under test. By utilizing a UWB THz power detector, a waveguide-based scalar transmission measurement system is demonstrated, a crucial step toward a future waveguide-based photonic VNA.

Photonic technologies bring intrinsic advantages in terahertz generation and detection, making them key enablers for a wide range of applications. However, currrent photonic-based terahertz receivers are limited in conversion loss compared to state-of-the-art electronic solutions. Here, we present the design, fabrication, and characterisation of an optoelectronic 220–330 GHz receiver, based on photonically-pumped Schottky barrier diodes (SBDs). The receiver integrates antiparallel low-barrier SBDs with a uni-travelling-carrier photodiode (UTC-PD) acting as the local oscillator (LO) signal generator. By combining these two components, the high-performance down-conversion provided by SBD-based mixers is paired with the photonic advantages in LO signal generation and distribution. A compact quasi-optical subharmonic receiver was fabricated and tested, achieving a minimum conversion loss of 18.1 dB. These results confirm the modelling process, since experimental results are in good agreement with simulations. Moreover, the receiver shows near-optimum performance for a pumping photocurrent as low as 5 mA, which proves the viability of the approach. While this work is an initial step with room for performance improvements, it highlights the potential of this solution to be used in applications like high-speed wireless communications, spectroscopy and imaging, and radio-astronomy.

This letter presents a high-performance corrugated horn for the sub-terahertz, manufactured monolithically using high-precision 3D printing technology based on Micro Laser Sintering (MLS) of stainless-steel powder. The horn features 45° inclined corrugation stubs that allow the building of the component with its axis vertical without any internal support structures. This ensures circular symmetry of the horn and high cross-polarization discrimination, and circumvents radiation performance degradation, typical of tilted printing. Departing from traditional designs, the horn also incorporates a rectangular-to-circular waveguide adapter, not only enhancing compactness but also avoiding errors and losses associated with assembly. The stainless-steel antenna was plated with gold. The prototype, measuring 10.8 mm × 10.8 mm × 29.7 mm, exhibits outstanding performance with a peak gain from 18 to 22 dBi, and >36 dB cross-polar discrimination over the frequency band of 145-225GHz. This is the first demonstration of 3D-printed corrugation structures in corrugated horns showing high performance beyond 100 GHz.

This work presents two manufacturing approaches for waveguide diplexers applicable to separating two of the G-band, 140-220 GHz, channels used in space borne radiometry of the Earth’s atmosphere. Waveguide diplexing is a lower volume alternative to a quasi-optical, i.e., frequency selective surface based, system. The two channels considered are 164-167 GHz and 175-191 GHz. The diplexer comprises a Y junction with two waveguide-cavity filters. Two high-precision fabrication technologies have been utilized: computer numerical control (CNC) machining and 3D printing. Two units were CNC machined as brass split-blocks and a third was 3D printed monolithically in stainless steel by a micro laser sintering process. The latter is an innovative structure that incorporates the diplexer with the waveguide flanges. All devices were gold coated to reduce loss. Measured insertion losses in the two channels were 0.6 and 0.34 dB for the CNC-machined diplexers and 1.8 and 0.8 dB for the 3D printed diplexer. The maximum frequency shifts from design were 0.695 GHz in the CNC-diplexers and 1.55 GHz in the 3D printed diplexer.

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

This paper presents a comprehensive evaluation of 3D-printed monolithic waveguide components fabricated by a high-precision micro laser sintering (MLS) process. The investigated devices are two 180 GHz bandpass filters and a straight G-band (140-220 GHz) waveguide section. All were made of stainless steel, which was later gold coated using an electroless process. One of the filter samples was characterized using X-ray micro-CT to inspect the printing quality as well as measure the internal dimensions. The sample was then sectioned to allow measurement of the surface roughness of the inner surfaces and inspect the gold coating quality. The as-manufactured stainless steel components showed high insertion losses: over 3 dB in the filter passbands and between 4.7 dB and 7 dB for the waveguide section, increasing with frequency over the G-band. This loss is due to the electrical conductivity of stainless steel as well as the surface roughness. Gold plating significantly reduced the insertion losses, to 0.5 dB for the filters and to between 0.6 dB and 1 dB for the waveguide section. The investigative study showed the high dimensional accuracy and good printing quality achieved by MLS, demonstrating the value of the technique in producing monolithic metal waveguide components with fine geometrics.

We report a $D$ -band waveguide diplexer, with two passbands of 130–134 and 151.5–155.5 GHz, fabricated using micro laser sintering (MLS) additive manufacturing with stainless steel. This is the first demonstration of metal 3-D printing technology for multiport filtering devices at a sub-terahertz (THz) frequency. For comparison, the same diplexer design has also been implemented using computer numerical controlled (CNC) milling. The diplexer, designed using coupling matrix theory, employs an all-resonator and $E$ -plane split-block structure. The two channels are folded for compactness. A staircase coupled structure is used in one channel to increase the isolation performance. The printed waveguide flanges are modified to adapt to the limited printing volume from the MLS. Effects of fabrication tolerance on the diplexer are investigated. An effective and unconventional electroless plating process is developed. The measured average insertion losses of the gold-coated diplexer are 1.31 and 1.37 dB, respectively. The respective frequency shifts from design values are 0.92% and 1.1%, and bandwidth variations are 4% and 15%. From a comprehensive treatment of the end-to-end manufacturing process, the work demonstrates MLS to be a promising fabrication technique for complex waveguide devices at a sub-THz frequency range.