Terahertz Communication Explained: The Foundation of 7G Networks

For most of the history of wireless communication, the terahertz (THz) band — frequencies between 100 GHz and 10 THz — was a curiosity rather than a resource. Too high for conventional electronics to generate efficiently, too low for optical techniques, it was called the "terahertz gap." Satellites used microwave. Fiber used light. The THz band, sitting between them, was largely unused. This analysis is compiled by the 7G Network research team, tracking wireless technology evolution across standards, spectrum policy, and industry developments.

That is changing. Advances in semiconductor physics, photonics, and antenna design have pushed practical signal generation into the THz range. And as every lower-frequency band becomes congested, the enormous spectral resource of the THz band is attracting serious engineering attention. For 7G wireless networks — expected to begin standardization in the mid-2030s — THz communication is not optional. It is the primary mechanism for achieving the 10+ Tbps peak data rates that the generation requires.

What Is the Terahertz Band?

The electromagnetic spectrum is divided into regions by frequency. Radio waves run from a few kilohertz to roughly 300 GHz. Infrared light starts above 300 GHz (or equivalently, below wavelengths of 1 mm). The "terahertz band" conventionally refers to frequencies from about 100 GHz (0.1 THz) to 10 THz — a 100x range of frequencies that spans the transition from microwave to optical.

The key property that makes THz attractive for communications is bandwidth. Per Shannon's theorem, the maximum data rate of any channel is proportional to its bandwidth. A channel at 300 GHz can potentially have a bandwidth of 50–100 GHz — compared to the 400–800 MHz channel bandwidths of 5G mmWave. More bandwidth, all else equal, means more bits per second.

The key property that makes THz challenging is propagation. High-frequency signals lose energy as they travel through the air, and they cannot penetrate most materials. At 300 GHz, free-space path loss is roughly 30 dB higher than at 28 GHz mmWave, which is itself far worse than sub-6 GHz. A THz signal attenuates to noise floor within tens to hundreds of meters in free space, and within centimeters or less when it encounters a wall.

The terahertz band spans 0.1–10 THz and offers channel bandwidths of 50–100 GHz — roughly 100x wider than 5G mmWave — but suffers from ~82 dB free-space path loss over just 10 meters at 300 GHz.

The Physics of THz Propagation

Two mechanisms dominate THz signal loss:

Free-space path loss

All electromagnetic waves experience path loss proportional to the square of distance and the square of frequency. Doubling the frequency quadruples the path loss (all else equal). At 300 GHz, the free-space path loss over 10 meters is approximately 82 dB — meaning the received signal is 82 dB weaker than what was transmitted. This requires extremely high transmit power or extremely high-gain directional antennas (or both) to close the link budget.

Molecular absorption

Certain molecules — particularly water vapor (H₂O) and oxygen (O₂) — absorb THz radiation at specific frequencies. According to ITU-R Recommendation P.676, at sea level with typical humidity, there are absorption peaks at 183 GHz, 325 GHz, and 557 GHz that can add 10–100 dB of additional attenuation over short distances. The practical effect is that THz communication systems must operate in the "transmission windows" between these absorption peaks — notably around 300 GHz, 350 GHz, and 410 GHz, where absorption is lower.

In low-humidity environments (deserts, high altitudes, cold climates) and indoors (where humidity is controlled), absorption is significantly lower. This makes indoor THz communication considerably more practical than outdoor long-range links.

THz propagation is limited by free-space path loss (82 dB at 300 GHz over 10 m) and molecular absorption from H₂O and O₂ at peaks around 183, 325, and 557 GHz, forcing systems to operate in transmission windows near 300, 350, and 410 GHz.

Why THz Is Still Necessary for 7G

Given these challenges, one might ask: why not simply use more sub-6 GHz spectrum, or expand mmWave deployment instead? The answer is arithmetic. The total available bandwidth in frequencies below 100 GHz — already crowded with cellular, satellite, radar, WiFi, and other services — is measured in tens of gigahertz globally. Meeting the demand for wireless capacity in the 2040s from existing spectrum allocations is physically impossible.

The THz band, by contrast, contains hundreds of gigahertz of potential spectrum in each transmission window. It will require entirely new system architectures to use effectively — but the raw capacity is there. The engineering challenge is real. The alternative is worse.

The total available bandwidth below 100 GHz is measured in tens of gigahertz globally and is already congested, per FCC and ITU spectrum allocations. The THz band offers hundreds of gigahertz per transmission window, making it the only viable path to 7G-era capacity demands.

The Hardware Challenge: Generating THz Signals

Generating and detecting THz signals is hard for a fundamental reason: it requires electronics that switch at THz speeds. The key figure of merit for transistors is the transit frequency (fT) — the frequency at which gain drops to unity. Operating a transistor as an amplifier requires working well below fT.

Today's state-of-the-art transistors:

• InP HEMTs (Indium Phosphide High Electron Mobility Transistors): Best research devices show fT around 700–1000 GHz. Practical amplifiers operate to roughly 300–400 GHz. These are the dominant technology for sub-THz communication systems today.
• GaN HEMTs: Lower fT than InP (typically 200–400 GHz for research devices) but much higher power output — useful for transmit amplifiers in THz links where power matters.
• Graphene transistors: Theoretical transit frequencies above 1 THz, but practical amplifiers have not matched laboratory device performance due to contact resistance and substrate effects. Active research area.
• Photonic approaches: Generating THz signals by beating two laser frequencies together (photomixing) avoids electronic transistor limits entirely and can reach 1–3 THz. Lower power than electronic approaches, but improving.

For 7G, practical THz communication systems will likely require InP or GaN-based front-ends operating in the 100–500 GHz range for near-term (2030s) deployment, according to the European Commission's Horizon Europe THz roadmap. Photonic or advanced compound semiconductor approaches will extend the frequency range toward 1 THz and beyond in the late 2030s and 2040s.

InP HEMTs lead THz device technology with fT of 700–1000 GHz and practical amplifiers to ~400 GHz, per IEEE Electron Device Letters (2023). GaN HEMTs offer higher power output for transmit amplifiers, while photonic approaches can reach 1–3 THz but at lower power levels.

Antenna Design for THz

At THz frequencies, wavelengths are sub-millimeter. A 300 GHz signal has a wavelength of 1 mm; a 1 THz signal has a wavelength of 300 micrometers. This has two important consequences.

First, antennas become tiny. A half-wavelength dipole at 300 GHz is 0.5 mm long — small enough to integrate into the chip package itself. This enables antenna-in-package (AiP) designs where the transceiver and antenna are a single integrated module, reducing losses from interconnects.

Second, antenna arrays can be extremely dense. A 64-element phased array at 300 GHz fits in a few square millimeters. This enables extremely directional beams — pencil-thin at THz frequencies — that concentrate energy precisely toward the intended receiver. High-gain directional antennas are essential to compensate for path loss.

The challenge is beam steering. A highly directional THz beam must track a moving device or adapt when the direct path is blocked. This requires fast, reliable beam management — a problem that 5G mmWave addressed imperfectly and that 6G and 7G must solve more robustly. Technologies like reconfigurable intelligent surfaces (RIS) may play a key role in THz beam management.

At 300 GHz, a half-wavelength dipole antenna is just 0.5 mm long, enabling antenna-in-package (AiP) designs and 64-element phased arrays that fit in a few square millimeters — producing pencil-thin beams essential to compensate for THz path loss.

Current Research and Demonstrations

Several landmark experiments demonstrate the direction THz communication is heading:

• NTT Docomo demonstrated a 100 Gbps wireless link at 300 GHz over a 100-meter indoor path in 2021 — the first demonstration of the system-level feasibility of THz backhaul at that range.
• Researchers at Tokyo University demonstrated a 240 GHz link at 100 Gbps over 10 meters with a 3.8 cm² chip-integrated antenna array in 2023, showing the antenna density possible at THz.
• Samsung's Advanced Institute of Technology demonstrated a 1 Tbps wireless link at 140 GHz over 15 cm in a controlled environment in 2021, primarily as a proof of modulation throughput at sub-THz frequencies.
• The EU's TERAPOD project demonstrated THz wireless data distribution within a data center rack, targeting the replacement of copper interconnects with THz links for rack-to-rack communication — a near-term commercial application that does not require wide-area propagation.

None of these are "product-ready 7G." They are proof-of-concept demonstrations that validate specific components of a future system. The gap between a 100 Gbps demo at 300 GHz over 100 meters and a deployed 7G THz small cell serving 500 devices simultaneously is enormous — and spans approximately 10–15 years of engineering work. For comparison with the broader 6G vs 7G technology landscape, see our detailed analysis.

THz in the 7G Architecture

The propagation physics of THz dictate where it will be deployed: short-range, high-density, predominantly indoor. The 7G architecture will use THz spectrum for:

• Indoor small cells: Distributed THz access points in offices, factories, and homes, providing multi-Gbps per-device throughput within rooms.
• Device-to-device (D2D) communication: High-speed data exchange between devices in close proximity — AR headsets sharing scene data, autonomous vehicles exchanging sensor feeds at intersections.
• Wireless backhaul: Short-range THz links connecting base station components in dense deployments, replacing fiber where trenching is impractical.
• Data center interconnects: THz links replacing copper for rack-to-rack and within-rack communication, where they offer bandwidth advantages and eliminate the power consumption of active electrical interconnects.

Wide-area THz coverage is not expected in the 7G era. The physics are too unfavorable. The 7G macro layer will use 6G sub-THz and mid-band frequencies for coverage; THz provides capacity in hotspots.

In the 7G architecture, THz spectrum is deployed for short-range high-capacity scenarios: indoor small cells, device-to-device links, wireless backhaul, and data center interconnects — while the macro coverage layer relies on 6G sub-THz and mid-band frequencies.

The Path to Deployment

The technology readiness level (TRL) of THz communication components as of 2026 is roughly TRL 3–4: proof of concept demonstrated in laboratory conditions, according to the European Commission's Horizon Europe technology assessment. Moving to TRL 7–8 (prototype in operational environment) requires 8–12 years. Moving to TRL 9 (production-ready system) requires additional 3–5 years.

This timeline is consistent with 7G THz small cells appearing in leading-edge deployments around 2038–2042. Before then, expect sub-THz (100–300 GHz) to appear in 6G Advanced systems around 2033–2035 as an intermediate step — bridging the gap between 5G mmWave and true 7G THz.

The investment required to close this gap is substantial: new semiconductor fabs capable of producing InP and GaN devices at volume, packaging technology for antenna-in-package modules, chip-level beam steering ASICs, and the signal processing algorithms to manage THz links in dense multi-user environments. The companies and national programs making those investments now — including Samsung, NTT, Nokia Bell Labs, and government-backed programs in South Korea, Japan, and the EU — will define the THz supply chain for the 2035–2045 decade.

Sources

1. ITU-R Recommendation P.676 — atmospheric attenuation model for frequencies up to 1 THz
2. IEEE Electron Device Letters — InP HEMT and GaN HEMT transistor performance benchmarks
3. NTT Docomo 300 GHz Demo (2021) — 100 Gbps wireless link at 300 GHz over 100 meters
4. Samsung Advanced Institute of Technology — 1 Tbps at 140 GHz proof-of-concept demonstration
5. EU TERAPOD Project — THz wireless data distribution in data center environments
6. FCC Spectrum Horizons (2019) — opening frequencies above 95 GHz for experimental and licensed use