What is the difference between passive DAS and active DAS?

Passive DAS uses only passive RF components — coaxial cable, splitters, combiners, directional couplers, and antennas — to distribute signal from a BTS or bi-directional amplifier, with no active amplification in the distribution network itself. Active DAS introduces amplification at distributed remote units (RUs) fed by fiber from a head-end unit, decoupling coverage area from signal-source location; RUs can be placed hundreds of metres from the master unit with negligible signal degradation.

How much loss does a 4-way splitter add in a passive DAS?

A 4-way splitter introduces approximately 7 dB of insertion loss, versus 3.5 dB for a 2-way splitter and 10.5 dB for an 8-way splitter. In a worked passive DAS link budget example at 800 MHz, a +33 dBm BTS feeding 20 m of LMR-400 trunk cable (−1.3 dB), a 4-way splitter (−7.0 dB), and 15 m of branch cable (−0.98 dB) yields an antenna port power of +23.7 dBm.

What antenna port power limit applies to DAS installations?

FCC Part 90 and carrier agreements typically limit radiated power to +24 dBm or less per antenna port to control interference. In the worked 800 MHz example, an antenna port power of +23.7 dBm plus 2.15 dBi antenna gain yields an EIRP of 25.85 dBm, which at 15 m from an omnidirectional antenna (FSPL ≈ 58 dB at 800 MHz) produces a received signal around −32 dBm.

What PIM level must a DAS pass during commissioning?

DAS commissioning requires a passive intermodulation (PIM) test at each antenna port using a ≥ +43 dBm two-carrier stimulus, verifying PIM products below −153 dBc, which is the 3GPP threshold. This is performed as part of the broader commissioning sequence that also includes a passive sweep of insertion loss and VSWR, a drive/walk test for RSSI, and data throughput verification.

What isolation is required between operators in a neutral-host DAS?

Neutral-host DAS arrangements require careful RF isolation between operators — typically greater than 30 dB port-to-port isolation in the combining network — along with SLA-driven performance monitoring. The FCC does not require individual neutral-host DAS licenses, but each mobile network operator's BTS must still operate under that operator's own existing spectrum license.

Engineering·13 min read·June 17, 2026

📡 Distributed Antenna System (DAS) Design for In-Building Wireless

End-to-end DAS design guide covering passive vs. active architectures, link budget methodology, multi-carrier/multi-band configurations, neutral-host considerations, and LTE/5G commissioning procedures.

📖Radio Communications — Illustrated Guide (Full Access)

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Why DAS Is Needed

Modern buildings present a hostile environment for outdoor macro-cell radio signals. Reinforced concrete, low-E glass, and metallic HVAC structures collectively attenuate signals by 20–35 dB. Underground parking garages, tunnels, and basements may receive no usable outdoor signal whatsoever. A Distributed Antenna System (DAS) solves this by distributing RF energy from a head-end signal source through a network of cables and small indoor antennas, achieving uniform coverage where a single macro antenna cannot.

Topics covered

DASdistributed antenna systempassive DASactive DASin-building wirelessiBwaveneutral-host DASLTE in-building5G DASBTSremote unitsplitter lossin-building coverage