IEEE AP-S TC-2 Workshop
Special Session Report: mm‑Wave and THz Circuits and Systems (EuMW 2025)
Introduction
The European Microwave Week (EuMW) 2025, held in Utrecht, the Netherlands, from 21 to 26 September 2025, hosted a variety of technical sessions devoted to emerging high-frequency technologies. One of these was Special Session EuMW02: “mm‑Wave and THz Circuits and Systems”, scheduled for 23 September 2025, 13:50–15:30 (CET) in the Mission 1 room at the Jaarbeurs convention center.
Session Chairs
The session was chaired by Prof. Dr. Hyunchul Ku (Konkuk University, Republic of Korea) and co‑chaired by Prof. Dr. Diego Caratelli (The Antenna Company and Eindhoven University of Technology, Netherlands).
Summary of the Session
The session focused on mm‑wave and THz circuits and systems to enable next‑generation communication, imaging, and sensing. mm‑wave (30–300 GHz) and THz (0.1–10 THz) frequencies offer enormous bandwidth for ultra‑high‑speed wireless links, radar, and spectroscopy, but they also pose stringent challenges due to severe free‑space path loss, limited output power of silicon electronics, and complex antenna integration. The session brought together researchers from academia and industry to address these challenges from complementary perspectives:
- Integrated transceivers for reflection‑mode terahertz imaging: The opening talk introduced concurrent transceiver pixel (CTP) arrays where an anharmonic oscillator functions as both transmitter and local oscillator, integrated with an on‑chip antenna. This architecture enables scalable reflection‑mode THz imaging with pixel sizes below half a wavelength and makes camera‑like focal‑plane arrays feasible.
- Scalable phased arrays above 100 GHz: Another contribution presented silicon‑based active phased arrays at 140 GHz and 220 GHz. The arrays employ a tiled multi‑chip architecture with on‑chip radiators and off‑chip antenna boosters to maintain high efficiency. Intermediate‑frequency (IF) beamforming is implemented within each element through co‑design of electromagnetics and circuits, achieving state‑of‑the‑art effective isotropic radiated power (EIRP) and demonstrating a 10 m wireless link.
- THz antenna design and measurements: A third presentation surveyed several 300‑GHz antenna array prototypes, including patch, Vivaldi, Yagi–Uda and slot arrays as well as a substrate‑integrated horn. The prototypes aim to balance high gain with low cost using printed‑circuit‑board (PCB) technologies, and a probe‑based compact antenna test range was described that enables simultaneous measurement of S‑parameters and 3‑D radiation patterns.
- Compound semiconductor technologies: Speakers from imec discussed the role of GaN and InP technologies in mm‑wave and sub‑THz front ends. GaN offers high breakdown voltage and efficiency but faces high substrate costs and integration challenges, while InP provides superior power‑added efficiency at D‑band frequencies (110–170 GHz) yet lacks scalability. Advanced heterogenous integration of these III‑V materials with CMOS via RF interposers and 3‑D stacking was highlighted to enable high‑performance yet cost‑effective solutions.
- Quasi‑optical antenna systems: The final talk provided an overview of quasi‑optical antenna arrays used originally for THz astronomy receivers. These systems employ lenses and reflectors to couple radiation efficiently at frequencies between 100 GHz and 600 GHz. With increased bandwidth demands, the same architectures are being adapted for high‑resolution radars and sub‑THz communication links, supported by high‑frequency electromagnetic models and prototypes.
Overall, the session emphasized that meeting the ambitions of 6G and beyond will require innovations across multiple levels of the system—from power amplifiers to antennas and quasi‑optical modules. Cross‑disciplinary collaboration between circuit designers, antenna engineers and materials scientists is essential to achieve high gain, low loss and scalability at frequencies above 100 GHz.
Program Summary
The five talks were delivered sequentially in 20‑minute slots. A summary of the program is given below:
| Time (CET) | Talk Title | Presenter(s) & Affiliation | Key Focus / Keywords |
|---|---|---|---|
| 13:50–14:10 | CMOS Compact Concurrent Transceiver Pixel Arrays for Terahertz Imaging Applications | Seoul National University; co‑authored with Kenneth K. O of the University of Texas at Dallas) | Concurrent transceiver pixels; on‑chip anharmonic oscillators; reflection‑mode THz imaging |
| 14:10–14:30 | Silicon‑based Scalable Active Phased Arrays above 100 GHz | Cheng Wang and colleagues (University of Electronic Science and Technology of China) | 140/220 GHz phased arrays; tiled multi‑chip architecture; IF beamforming; high EIRP |
| 14:30–14:50 | THz Antenna Designs and Measurements | Yu‑Hsiang Cheng (National Taiwan University) | 300‑GHz antenna prototypes (patch, Vivaldi, Yagi–Uda, slot, horn); compact test range; low‑cost PCB technologies |
| 14:50–15:10 | Compound Semiconductor Technologies for mm‑wave and sub‑THz Applications | Compound Semiconductor Technologies for mm‑wave and sub‑THz Applications | GaN and InP semiconductors; integration with CMOS via RF interposers and 3‑D stacking; applications in extreme data‑rate wireless, high‑speed wireline, radar and imaging |
| 15:10–15:30 | Quasi‑Optical Antenna Systems: From Space to Widespread Sub‑THz Applications | Nuria Llombart Juan (TU Delft) | Quasi‑optical antenna arrays using lenses/reflectors; adaptation from astronomical receivers to communication and sensing; prototypes up to 600 GHz |
Biographical Notes
- Wooyeol Choi is an associate professor of Electrical and Computer Engineering at Seoul National University. He earned his Ph.D. from SNU in 2011 and previously worked at the University of Texas at Dallas and Oklahoma State University. His research focuses on integrated circuits and systems for RF through THz frequencies.
- Cheng Wang holds degrees from Tsinghua University and MIT. He served as a research scientist at Analog Devices and is now a professor at the University of Electronic Science and Technology of China. His interests span cryogenic CMOS circuits, molecular clocks and silicon‑based mm/THz phased arrays.
- Yu‑Hsiang Cheng completed his Ph.D. at MIT in 2019 and is currently an assistant professor at National Taiwan University. He researches terahertz electronics and ultrafast spectroscopy and chairs the IEEE AP‑Society Taipei Chapter.
- Yu‑Hsiang Cheng completed his Ph.D. at MIT in 2019 and is currently an assistant professor at National Taiwan University. He researches terahertz electronics and ultrafast spectroscopy and chairs the IEEE AP‑Society Taipei Chapter.
- Nuria Llombart Juan, a full professor at TU Delft, is editor‑in‑chief of the IEEE Transactions on Terahertz Science and Technology. She holds MSc and PhD degrees from the Polytechnic University of Valencia and has worked at Fraunhofer IIS, TNO, the Jet Propulsion Laboratory and Complutense University. Her research on antennas and THz systems has earned numerous awards, including the IEEE MTT‑S THz Best Paper Award and an ERC Starting Grant.
Overall Significance
The session underscored that mm‑wave and THz technologies are rapidly maturing, driven by the prospect of multi‑gigabit wireless links, high‑resolution radar and spectroscopic applications in 6G and beyond. Achieving these goals requires co‑design across circuits, antennas, and materials, as demonstrated by the five complementary talks. The presenters highlighted both technological breakthroughs and remaining challenges—such as scaling of phased arrays, low‑cost high‑gain antennas, efficient power amplifiers, and advanced packaging—that will guide research in the coming years.
