Guest Editorial: Antennas and propagation at millimetre, sub‐millimetre wave and terahertz bands

A revolutionary enhancement of transmission data rates is required to meet the challenge an exponential capacity increase for sixth generation (6G) and beyond mobile communication sensing systems in era 2030 beyond. This generates a strong motivation exploring underutilised millimetre wave (30–300 GHz), sub-millimetre (300–3000 terahertz (0.1–10 THz) bands. These frequencies offer great opportunities device miniaturisation thanks short wavelengths fostering compact, high gain antennas abundance spectrum variety future applications. However, preserving good performance with ever-decreasing form factor under ever-increasing interference scenarios making complicated task antenna design even more complex. Moreover, synergism susceptibility molecular absorption, changed relationships between dimensions objects, ultra-broadband bandwidths, results propagation at (mmWave), sub-mmWave, (THz) bands distinguished from microwave frequencies. The current Special Issue focused on research ideas, articles, experimental studies mmWave, THz bands, priority considering contributions 90 100 GHz higher. In this Issue, we have received 22 papers, all which underwent peer review. Ten high-quality been selected strict review process supported by reputed international experts. They can be clustered into three main categories, namely band, mmWave paper laying first category exhibit novelties Xu et al. second papers offers advanced cutting-edge technologies, such as shared slotted waveguide arrays metasurfaces. are Wang al., Huang Zhang al, Peng last investigates channel characteristics sub-THz explore potential applications these Doeker Lee Yue brief presentation each follows. present discovery approach using ray tracing combined iterative fine tuning. By evaluating impact characteristics, it shown that sidelobes lead error final alignment highly directive due superposition power via multipath components, equations calculate maximum given. Besides, evaluated respect sidelobe suppression. Here, given do not affect if than 30 dB lower mainlobe. different on-chip Complementary metal-oxide-semiconductor (CMOS) technology detector source. For detector, multi-band dual-ring structure miniaturised circular diamond structures designed. At frequency 300 GHz, 600 800 ring 5.7 dBi, 7.2 dBi respectively. 5.3 5.96 GHz. source, rectangular-slot T-slot designed 2.92 3.87 effectiveness verified measurement indicates proposed CMOS W-band dual-beam low side-lobe level radiating layer. consists symmetrical dual ports feed network layer located two sides antenna, novel 4 × 32 array radiation layer, bottom Based results, has 24.8 far-field gain, −17/−25.5 E/H plane side lobe level, 19.8° beam deflection 94 performances were agreement other, measured isolation was above 14.5 24 circularly polarised (CP) metasurface rectenna wireless transmission. Measurements show 11.3 dBic axial ratio 2.5 CP conversion efficiency profile, conformal electrical equipment. It suitable systems. multiple lens-based compact test ranges (CATRs) simulate angles arrival base-stations radio resource management (RRM) measurement. Composed lens phase 2 emission electromagnetic signals, only four CATRs create conditions six arrival. Validated through simulations measurements, worst-case amplitude variation quiet zone region ±0.8 26 ±7.5° zone, could used fifth-generation (5G) RRM propose printed ridge gap (PRGW)-based broad bandwidth aperture. To validate reflection performance, prototype fabricated followed verification. Measurement −10-dB impedance 14.3% (26.0–30.0 GHz) realised prototype. Furthermore, cross polarisation (XP) quite low, average 9.8 obtained. provide analyses multi-frequency based wideband measurements 28, 38, 71, 82, 159 emphasis (i.e. characteristics. All conducted same cubicle office room environment locating transmitter receiver positions. path loss shadow fading significant differences depending range 28 delay spread shows generally decreasing trend increases. observations findings will useful development 5G and/or 6G networks rain attenuation prediction model terrestrial line-of-sight links, particularly frequency. total described accounts wet attenuation. addition, rainfall rate adjustment proposed. root-mean-square 21.54% prediction, improvement compared other existing models. Because approaches 1 distances, applied short-distance links. assist designers link margins accurately. analyse channels Hyperloops ray-tracing method. simulation mainly affects large-scale parameters, but little influence small-scale parameters. Consequently, vacuum tube significance Hyperloop train-ground system design. introduce basic principle hybrid beamforming its unique features. First, angular orthogonality obtained exploiting spatially sparse nature channel. Then, typical studied, includes single-user/multi-user system, integrated energy transfer intelligent reflecting surface aided system. Some exemplary demonstrate advantage our THz. last, open challenges provided stimulating interest. first-hand information state art technologies modelling understanding behaviour corresponding designs pave way towards realisation challenging Guest Editors would like thank authors their submissions reviewers reviews helpful suggestions improving content papers. We also extend sincere journal's Editors-in-Chief Editorial Office providing us opportunity organise supporting throughout whole process. Finally, guest editors wish you enjoyable reading Issue. Ke Guan (Senior Member, IEEE) B.E. degree Ph.D. Beijing Jiaotong University 2006 2014 He Full Professor State Key Laboratory Rail Traffic Control Safety & School Electronic Information Engineering, University. 2016, he awarded Humboldt Research Fellowship Postdoctoral Researchers. Visiting Scholar Universidad Politécnica de Madrid, Spain 2009 2013. From 2011 2013 2016 2018, Institut für Nachrichtentechnik (IfN) Technische Universität Braunschweig, Germany. February 2023 July 2023, Wien, Austria. authored/coauthored books five book chapter, 200 journal conference ten patents. His interests include channels, high-speed railway communications, machine learning digital twin environments various complex scenarios, vehicle-to-x systems, space-air-ground networks. Dr. pole leader EURNEX (European Railway Network Excellence). recipient International Union Radio Science (URSI) Young Scientist Award. 14 Best Paper Awards, including IEEE vehicular society Neal Shepherd memorial best award 2019 2022. Editor Vehicular Technology Magazine IET Microwave, Antenna Propagation, Transactions Communication Magazine. serves Publicity Chair PIMRC Co-Chair ITST Track EuCNC, Liaison EUSIPCO 2019, Session Convener EuCAP 2015-2022, TPC Member many conferences, Globecom, ICC VTC. delegate 3GPP member IC1004, CA15104, CA20120 initiatives. Wilhelm Keusgen his Dipl.-Ing. Dr.-Ing. degrees RWTH Aachen 1999 2005 2004, Institute High Frequency Technology, University, where worked frontend millimetre-wave antennas, reciprocity MIMO 2004 2021, headed group transceiver Fraunhofer HHI. Since Berlin. areas communications beyond, MIMO, full duplex, impairments compensation. published 130 scientific Wei Fan Aalborg (AAU), Denmark 2014. directly promoted assistant professor after graduation then tenured associate August 2017. admitted promotion program March 2023. holds Docentship ‘Radio Propagation OTA Testing Methodologies’ Oulu, Finland since Jan currently leads ‘wireless over-the-air (OTA) testing’ AAU. Cesar Briso director Radiocommunications Group Technical SPAIN. 30-year trajectory, initially study circuits radar, 20 years transportation especially speed trains, metropolitan railways Unmanned aerial Vehicles. On 2010 started working critical 5G. topic done relevant years, several publications collaborations experts Europe, China USA. managed 23 national projects hold patents Now project: ‘Next Generation Train Communications Systems’, inside Chinese ‘The Belt Road’. author 40 participated 60 congress. editor 6 transportation. National prizes research. Bo Sun senior specialist standardisation Sanechips Co., Ltd. implementation, IoT next etc. proactive standard honored contribution awards 802.11 standards. PHY adhoc co-chair TGax successfully developed 802.11ax (a.k.a. Wi-Fi 6). Now, chair TGbd Next V2X) AMP SG. NITS SC41 (IoT) WG2 (Networking Communications).