TL;DR
- Spectrum is the range of radio frequencies over which mobile signals travel; each band has distinct propagation characteristics that determine coverage and capacity.
- Low-band spectrum (below 1 GHz) travels furthest and penetrates buildings best, making it essential for rural and indoor coverage.
- Mid-band spectrum (1–6 GHz) balances coverage and speed; the 3.4–3.8 GHz range is the primary workhorse of 5G in the UK.
- High-band (millimetre-wave, above 24 GHz) offers very high capacity but extremely limited range, suited to dense indoor venues.
- Ofcom licences spectrum through competitive auctions and may attach coverage obligations to ensure rural areas are served.
What spectrum is and why it matters
Radio spectrum is a finite portion of the electromagnetic spectrum — the frequencies between roughly 30 kHz and 300 GHz that can carry information wirelessly. Mobile operators require exclusive use of defined frequency bands within a geographic area to avoid their signals interfering with each other. Without licensed spectrum, the radio environment would be chaotic, with competing signals drowning each other out. Spectrum is therefore one of the most economically significant inputs into running a mobile network, and access to the right combination of bands shapes the quality of service a network can offer.
In the UK, spectrum management is carried out by Ofcom under powers granted by the Wireless Telegraphy Act 2006. Every frequency range has a designated primary and, in some cases, secondary use — recorded in the UK Frequency Allocation Table, a document Ofcom publishes and updates. Mobile cellular services occupy a relatively small slice of the overall spectrum, but the bands involved are among the most commercially valuable because of the scale of consumer demand they serve.
Low-band spectrum: coverage first
Frequencies below 1 GHz — including the 700 MHz, 800 MHz and 900 MHz bands — are prized for their propagation characteristics. Radio waves at these frequencies travel tens of kilometres from a single base station and diffract around terrain, meaning one mast can cover a large rural area. They also penetrate building materials more effectively than higher frequencies, improving indoor reception. In the UK, the 800 MHz band (part of the digital dividend released when analogue television was switched off) was auctioned by Ofcom in 2013 and has been used primarily for 4G coverage in rural and suburban areas.
The 700 MHz band, another digital dividend, was auctioned in 2021 and is being deployed for both 4G and 5G. Coverage obligations attached to this auction required operators to serve specified percentages of the UK landmass, a mechanism Ofcom uses to ensure spectrum serves the public interest rather than only commercially attractive areas. Low-band 5G over 700 MHz does not deliver dramatically higher speeds than 4G in practice, but it extends 5G’s geographic footprint significantly.
Mid-band spectrum: the 5G workhorse
The mid-band range, broadly 1–6 GHz, contains several important mobile allocations. The 1800 MHz and 2100 MHz bands have long supported 4G LTE. The most significant recent addition is the 3.4–3.8 GHz “C-band,” which Ofcom auctioned in 2018. This band offers substantially more contiguous spectrum than lower bands, enabling operators to use wider channel bandwidths that translate directly into higher data throughput. Most UK 5G services visible to consumers today operate primarily on 3.4–3.8 GHz.
The trade-off with mid-band is reduced range compared to sub-1 GHz frequencies: a 3.5 GHz cell typically covers a smaller radius than an 800 MHz cell from the same mast height. Operators therefore need denser networks of base stations to achieve contiguous mid-band coverage in urban areas. The 2.3 GHz band, also auctioned in 2018, adds further mid-band capacity. Upcoming allocations in the 26 GHz range will transition into millimetre-wave territory.
| Band Category | Frequency Range | Coverage Radius (typical) | Peak Speeds (indicative) | Primary UK Use |
|---|---|---|---|---|
| Low band | 700 MHz, 800 MHz, 900 MHz | Up to ~10–20 km rural | Lower; suitable for voice and basic data | Rural 4G/5G coverage, indoor penetration |
| Mid band (1–3 GHz) | 1800 MHz, 2100 MHz, 2300 MHz | 1–5 km urban | Moderate to high; mainstream 4G capacity | Urban/suburban 4G capacity layer |
| Mid band (3–6 GHz — C-band) | 3400–3800 MHz | 0.5–2 km urban | High; typical 5G commercial speeds | Primary 5G layer in UK cities |
| High band (mmWave) | 26 GHz and above | 100–300 m (line of sight) | Very high peak; multi-Gbit/s possible | Dense venues, industrial, early deployment |
High-band (millimetre-wave) spectrum
Millimetre-wave (mmWave) frequencies — broadly 24 GHz and above, including the 26 GHz band Ofcom has been consulting on for UK deployment — offer vast amounts of available bandwidth. A single 5G channel in mmWave spectrum can be hundreds of megahertz wide, enabling peak data rates measured in gigabits per second. This makes mmWave spectrum extremely attractive for high-density scenarios such as sports stadia, convention centres, and some industrial automation applications.
The fundamental constraint is physics: signals at 26 GHz travel only a few hundred metres and are blocked by walls, windows and even heavy rain. This severely limits their usefulness for outdoor wide-area coverage. UK operators have conducted mmWave trials, and Ofcom published a consultation in 2023 on making the 26 GHz band available for 5G. Its practical role in the UK is likely to remain confined to targeted deployments rather than forming the basis of any operator’s primary network.
How Ofcom auctions spectrum
Ofcom uses competitive auctions to award new mobile spectrum licences, intending to allocate spectrum to the parties that value it most and will use it efficiently. Before an auction, Ofcom publishes detailed information memoranda setting out the available lots, the frequency ranges, and any licence conditions. Bidders (which must be eligible legal entities, typically licensed telecoms operators) submit bids through a structured multi-round process. Award prices for contested mobile spectrum have historically reached billions of pounds in aggregate across the major UK auctions held in 2013, 2018 and 2021.
Spectrum licences are not perpetual: they are awarded for defined terms, and Ofcom can attach conditions requiring coverage of specified population or geographic area thresholds. These obligations are a tool for ensuring that commercially marginal areas — particularly rural Scotland, Wales and Northern Ireland — receive investment. Ofcom also permits secondary trading of spectrum licences, allowing operators to buy, sell or lease frequencies after the initial award, which provides flexibility as network strategies evolve.
Why operators use multiple bands simultaneously
No single frequency band delivers optimal performance in all circumstances. A large UK mobile operator therefore typically holds spectrum across low, mid and possibly high bands, deploying them in combination. Low-band frequencies form the “coverage layer,” ensuring that even rural and indoor locations receive a usable signal. Mid-band frequencies provide the capacity layer in towns and cities, handling the bulk of data traffic. Where mmWave is deployed, it functions as a hotspot layer for extreme-density locations.
Modern handsets and networks use carrier aggregation — combining multiple spectrum blocks simultaneously — to deliver speeds higher than any single band could provide alone. A 5G device might aggregate a 700 MHz channel with a 3.5 GHz channel to achieve both broad coverage and high throughput. This multi-band approach means the network topology is considerably more complex than a single-frequency system, but it allows operators to serve a much wider range of use cases from one physical infrastructure.
What this means in practice
Marcus lives in a market town in rural Shropshire. His operator holds licences at 700 MHz (5G coverage layer) and 3.5 GHz (5G capacity). At home, his 5G phone connects on 700 MHz because the nearest 3.5 GHz cell is several kilometres away; he gets 5G coverage but speeds in the region of 30–80 Mbit/s rather than the 200–400 Mbit/s his colleague enjoys in Birmingham where 3.5 GHz cells are dense. When Marcus visits Birmingham for a meeting and opens a large file in a hotel conference room, his phone automatically aggregates both bands, climbing well above 200 Mbit/s. The frequency band his phone uses at any moment is invisible to him, but it is the direct result of Ofcom’s spectrum allocation decisions and his operator’s deployment choices.
Related Guides
How we verified this
This article draws on Ofcom’s spectrum management publications and auction information memoranda, the UK Frequency Allocation Table, the Wireless Telegraphy Act 2006 (legislation.gov.uk), Ofcom’s Connected Nations reports, and Ofcom’s 2023 consultation documentation on the 26 GHz band for 5G use.
Disclaimer: Kaeltripton.com is an independent UK editorial publisher. We are not regulated by Ofcom or the FCA and we do not sell or arrange mobile services, insurance, or financial products. This content is for general information only and is not legal, financial, or technical advice. Rules, prices, and operator policies change. Verify the current position with Ofcom, GOV.UK, the ICO, or your provider before acting. ICO registered ZC135439. Last reviewed: 2026-06-05.
Frequently Asked Questions
What is mobile spectrum?
Mobile spectrum refers to the specific radio frequency bands licensed to mobile network operators for wireless communication. It is a finite national resource — different frequency ranges have different physical properties affecting how far signals travel and how much data they can carry. In the UK, Ofcom allocates and licences spectrum under the Wireless Telegraphy Act 2006, and operators pay substantial sums at auction to secure exclusive use of particular bands within the UK.
Why do operators use different frequencies?
Different frequencies offer different trade-offs between coverage range and data capacity. Low frequencies (e.g. 700 MHz) travel far and penetrate buildings well, making them suitable for rural and indoor coverage. Higher frequencies (e.g. 3.5 GHz) carry more data but have shorter range. Operators use multiple bands simultaneously — a technique called carrier aggregation — to deliver broad coverage and high capacity across different environments within a single network.
How is mobile spectrum allocated in the UK?
Ofcom allocates mobile spectrum primarily through competitive multi-round auctions, in which eligible operators bid for lots of frequency spectrum. Before each auction, Ofcom publishes licence conditions including any coverage obligations operators must meet. After the award, operators may also trade spectrum licences with each other under Ofcom’s secondary trading framework. Major UK spectrum auctions took place in 2013, 2018 and 2021, covering bands used for 4G and 5G services.
What is the difference between low band and high band 5G?
Low-band 5G (such as 700 MHz) extends 5G coverage into rural and indoor areas but delivers speeds broadly comparable to good 4G because narrower channel widths limit throughput. High-band 5G (millimetre-wave, 26 GHz+) can deliver multi-gigabit peak speeds but only within a very short range and with poor building penetration. Most UK consumers currently experience mid-band 5G at 3.4–3.8 GHz, which balances reasonable coverage with substantially higher speeds than 4G in congested areas.
Who manages spectrum in the UK?
Ofcom is the UK’s statutory spectrum management authority, acting under powers in the Wireless Telegraphy Act 2006 and the Communications Act 2003. It publishes the UK Frequency Allocation Table, runs spectrum auctions, issues licences, monitors compliance and can revoke or vary licences. Ofcom coordinates with international bodies — including the International Telecommunication Union (ITU) and the European Conference of Postal and Telecommunications Administrations (CEPT) — to ensure UK spectrum use aligns with global frameworks.
