Demand for wireless connectivity is rising exponentially. As requirements for speed, capacity and reliability grow, engineers and researchers are pushing beyond today’s mobile technologies to explore new frontiers in the electromagnetic spectrum. Two promising candidates for future wireless technologies are millimetre wave (mmWave) and the terahertz spectrum (THz). Both sit in the high-frequency wireless end of the spectrum and promise extraordinary capabilities, but they also bring challenges. Understanding the differences, and how they might work together, is a task that the Hub in All Spectrum Connectivity (HASC) is fully embracing.

What are mmWave & THz?

The electromagnetic spectrum is divided into frequency bands. The higher the frequency, the shorter the wavelength and the more data that can be carried, though this often comes with greater transmission challenges.

• mmWave typically refers to frequencies between around 24 and 300 GHz, with wavelengths measuring between 1 and 10 mm. mmWave is already being commercially deployed in US 5G networks (with the UK moving towards implementation) and is a core part of the discussion around 6G.
• THz generally refers to frequencies from 100 GHz up to 10 THz (10,000 GHz), with wavelengths between 3 mm and 30 µm. This range offers a very large bandwidth and high-capacity transmission, making it a key candidate for meeting the data demands of future network applications.

Since the ranges of mmWave and THz overlap, the boundaries between these are not always rigid, and their characteristics can sometimes blur.

The Similarities and Differences of mmWave & THz

As mmWave and THz are both high-frequency bands, they share many fundamental traits. These include:

• High transmission loss: signals weaken quickly as they travel, which limits range and requires more transmitters or repeaters.
• Poor penetration: walls, furniture and even human bodies can block or absorb the signal, making indoor coverage difficult.
• Line-of-sight requirement: reliable links often need a clear path between the transmitter and receiver, as signals do not bend easily around obstacles.
• Environmental sensitivity: conditions such as rain, humidity or atmospheric absorption can further reduce performance.

However, mmWave and THz also have key differences:

• Data rates: whilst mmWave could deliver high-speed connectivity to modern networks, the capabilities of THz far exceed this, with the potential for ultra-high data rates exceeding 100 Gbit/second.
• Propagation and loss: THz frequencies experience even higher propagation loss than mmWave. This means that while they can transmit vast amounts of data, their range is more limited.
• Penetration: both mmWave and THz have significantly lower penetration than radio frequencies. However, whilst mmWave can penetrate certain materials such as glass with manageable loss, THz waves penetrate much more weakly and are mostly restricted to direct, unobstructed paths.

In short: mmWave can travel further, while the THz spectrum can deliver more data over shorter distances.

Use Cases: Today and Tomorrow

mmWave today: mmWave is already finding its place in commercial systems. Telecoms are integrating mmWave into mobile networks to boost capacity and deliver faster wireless experiences. For users, this means higher speeds in dense urban centres, stadiums or transport hubs where data demand is extremely high.

Emerging THz applications: THz is currently much less commercially developed, but global interest and research is expanding rapidly. Potentially, THz in telecommunications could:

• Replace short stretches of fibre optic cable, especially in areas where fibre installation is impractical or costly (for instance, across rivers or challenging terrain), or where fibre networks have been damaged during disasters such as earthquakes.
• Enable short-range high-speed comms in data centres, where stable, ultra-fast links are essential.
• Support advanced applications such as holographic conferencing or virtual reality/ augmented reality environments.

The exciting part is how the two might work together: mmWave providing robust, wide-area coverage, while THz delivers extreme data rates for high-capacity, short-range applications.

Challenges and Innovation

The main challenge for both mmWave and THz is overcoming the physical limitations of high-frequency signals, in particular, the fact they lose power quickly and don’t diffract around or penetrate obstacles well. Researchers are tackling these hurdles on multiple fronts:

• Device engineering: building transmitters and receivers capable of generating and handling such high frequencies efficiently.
• Hybrid integration: combining THz wireless with existing optical fibre infrastructure to extend range and resilience.
• Algorithms and adaptation: designing systems that adapt dynamically to user movement and channel conditions, ensuring reliable connections even in difficult environments.

HASC Research Spotlight

At HASC, researchers are working to address key unknowns about the use of mmWave and THz in telecommunications. This has included measuring and modelling the performance of mmWave signals and their ability to deliver ultra-reliable WiFi in factory settings, and demonstrating the generation of precise THz signals by combining two different laser signals (known as photo-mixing) a technique which could reduce the implementation and operation cost of a THz communications system.

A strong focus is the integration of THz wireless with fibre networks to create seamless, end-to-end systems. For example, HASC researchers at UCL, in conjunction with German colleagues, have demonstrated a fully-optoelectronic 300 GHz wireless link, achieving up to 180 Gbps over 1.5 metres. This was done by mixing optical signals in order to generate and receive THz wireless signals. Such experiments show how fibre and THz wireless can be combined, paving the way for networks that are faster, more flexible and more efficient.

The Future: Complement, Not Compete

Looking ahead, it is unlikely that the future will be one of mmWave vs THz; instead of competing, these will complement one another:

• THz will excel in scenarios demanding extreme data rates over short distances, such as data centres or specialised industrial environments.
• mmWave will continue to support mobile users who need higher speeds than 4G/5G mid-bands can provide, while accommodating movement and broader coverage.

Together, mmWave and THz will form part of a flexible, multi-band ecosystem. This is central to HASC’s vision: an integrated network of wired and wireless systems, dynamically adapting to user needs. Through our research programmes and by brokering exchange between academia, industry and policy, HASC is working to accelerate the transition to a high-frequency wireless future.

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