When do you need an external antenna?
External antennas are needed when the integrated antenna in your router or indoor CPE does not capture sufficient signal for adequate performance. This applies most commonly in three situations: marginal coverage areas, properties with signal-attenuating construction materials (concrete, metal cladding, cavity fill insulation), and indoor router positions that are far from an exterior wall.
An external antenna mounted outside the building captures the 5G signal before it is attenuated by building materials. The improvement in received signal power compared to an indoor antenna is typically 10-20 dB. In signal quality terms, that difference can take a connection from marginal and unstable to reliable and fast.
Types of external 5G antenna
Directional MIMO panel antennas focus gain in one direction – toward the serving mast. They are used when your mast is in a known direction and you want maximum gain toward it. Typical gain is 7-12 dBi per element. A directional antenna pointed accurately at the mast will outperform an omnidirectional on the same connection.
Omnidirectional MIMO antennas receive from all directions, which is useful when you are unsure which direction your serving mast is in, or where your router may switch between masts from different directions. Lower gain than directional but more tolerant of uncertain mast location.
Outdoor CPE units are not strictly antennas – they are complete modem, antenna and processing units in a weatherproof housing. They deliver better performance than a separate antenna plus indoor router in most cases, at the cost of a more complex installation. See our indoor vs outdoor CPE guide.
Key antenna specifications
Frequency band coverage: The antenna must cover the 5G bands your operator deploys. For UK n78 (3.5 GHz), an antenna specified for the 3.3-3.8 GHz range is needed. For n28 (700 MHz), coverage of 600-900 MHz is required. Many wideband 5G MIMO antennas cover 600 MHz to 6 GHz in a single unit.
MIMO configuration: A 2×2 MIMO antenna has two antenna elements and two coaxial connections. Match the MIMO configuration to your router’s antenna ports (2×2 for two ports, 4×4 for four).
Gain: Measured in dBi. Higher is not always better for an omnidirectional antenna, as very high gain omnidirectionals trade off elevation angle coverage for horizontal gain. For directional panel antennas, 8-12 dBi is typical and appropriate for most FWA use.
Connector type and cable: Most routers use SMA or TS9 external antenna connectors. Confirm your router’s connector type before purchasing. Cable quality matters for high frequency signals: LMR-195 or LMR-400 are appropriate for 5G frequencies. Thin RG58 cable has significant loss at 3.5 GHz and should be avoided for any run over 1-2 metres.
Installation guidance
Mount the antenna as high as practical, on the building face that most directly faces your serving mast direction. If you are unsure of the mast direction, use a site like Mastdata or Ofcom’s mast register to identify your nearest 5G sites and plan the antenna orientation accordingly.
Keep cable runs as short as practical. Signal loss in coaxial cable at 3.5 GHz is significant: LMR-195 loses approximately 0.6 dB per metre. A 10 metre cable run costs you around 6 dB – equivalent to more than halving your received signal power. Use LMR-400 or equivalent low-loss cable for runs over 5 metres.