In-Building Coverage: DAS and Repeater Antenna Systems Explained

Reinforced concrete, structural steel and energy-efficient glazing are all effective radio frequency attenuators. The buildings that house modern emergency services, transport control rooms, data centres and industrial operations are often the buildings most likely to have inadequate coverage for the radio systems that matter most inside them. Distributed Antenna Systems (DAS) and repeater installations solve this problem by bringing a signal source inside the structure and distributing it to where it is needed.

Passive DAS

A passive DAS uses the external antenna feed from a base station or repeater, splits it, and distributes it through coaxial cable to a network of internal antenna elements. No active amplification is used within the distribution network itself. Passive DAS is well-suited to medium-sized buildings where the cable runs are short enough that losses remain within acceptable limits. The main advantage is simplicity and reliability — there are no active components in the distribution path to fail. The main limitation is that cable loss accumulates quickly in large buildings, limiting the coverage radius achievable from each tap point.

Active DAS

An active DAS converts the RF signal to optical or ethernet-carried digital format, distributes it through fibre or network cable to remote antenna units, and reconverts it to RF at each unit. This allows the signal to be distributed across very large buildings or multi-building campuses without the cable loss constraints of passive systems. Active DAS is the standard for large venues, hospitals, airports and high-rise buildings. It is significantly more complex to design and commission than passive DAS, and requires active hardware at each remote antenna unit.

Repeater Systems

A repeater takes a signal received from an external donor antenna, amplifies it and retransmits it inside the building. For TETRA and PMR applications, repeaters are widely used for relatively straightforward in-building coverage challenges. The external donor antenna needs clear line of sight to the serving base station; the internal coverage antennas distribute the amplified signal within the building. Key design considerations are donor signal quality, isolation between the donor and internal antennas to prevent oscillation, and ensuring the repeater's operating band matches the network in use.

Antenna Selection for In-Building Systems

For internal coverage distribution, omnidirectional ceiling-mount antennas are used in open areas; panel antennas provide coverage in corridors and stairwells. Internal antennas in DAS and repeater systems are low-power devices — the coverage comes from quantity and placement rather than individual antenna gain. Antenna positions should be planned to ensure overlapping coverage with no dead spots, verified by a post-installation RF survey.

Contact Renair to discuss in-building coverage antenna requirements: renair.co.uk/contact-us.

Frequently Asked Questions

Do I need planning permission for an in-building antenna system?

Internal antenna systems generally do not require planning permission. Donor antennas mounted externally on a building may require permission depending on size, location and the building's listed status or conservation area context. For emergency services buildings, permitted development rights often apply — but local authority confirmation is advisable.

Can a DAS support multiple radio systems at once?

Yes. A well-designed DAS can distribute signals from multiple services simultaneously — TETRA, LTE/ESN, PMR, cellular — using the same antenna infrastructure. This is a key advantage of active DAS systems in large venues that need to support both emergency services and public cellular connectivity.

What is the typical coverage radius of a single internal antenna in a DAS?

In a typical open-plan office environment, a single ceiling-mount internal antenna covers around 10–15 metres radius. In heavy construction — reinforced concrete walls, thick steel partitions — this may reduce to 5–10 metres. A detailed site survey and propagation assessment is required to determine antenna placement for any real installation.