Leaky Feeder Cable: Applications & Function
A leaky feeder cable (often called a radiating cable) is designed specifically to provide two-way radio, cellular, or Wi-Fi coverage in confined spaces where standard radio waves cannot reach or easily propagate. It functions as a continuous, distributed antenna. Instead of radiating from a single point, it emits and receives RF signals along its entire length.
Specific Applications
Because signals like VHF, UHF, and cellular bands require line-of-sight and are easily blocked by dense materials, leaky feeders are essential in environments that act like natural Faraday cages or block RF propagation:
- Underground Mines and Tunnels: This is the most common use. If you put a standard antenna at the entrance of a subway, road tunnel, or mine shaft, the signal will drop off as soon as the tunnel curves. Running a leaky feeder along the ceiling guarantees continuous coverage for emergency responders, train operators, and passenger cell phones.
- Large Buildings and Skyscrapers: They are often used in elevator shafts, underground parking garages, and internal corridors as part of an in-building Distributed Antenna System (DAS) to eliminate dead zones.
- Aviation and Maritime: They are routed through the metal hulls of ships and aircraft to provide internal wireless networks for the crew without signals bouncing erratically around the metal bulkheads.
- Industrial Plants: In facilities with massive amounts of dense machinery, pipes, and metal grids, leaky feeders snake through the infrastructure to maintain reliable communication for maintenance teams.
How It Works
Physically, a leaky feeder looks very similar to standard coaxial cable.
In a standard coax, the copper core carries the RF signal, and the outer metallic shield is designed to be perfectly solid. The shield’s job is to keep 100% of the RF energy trapped inside the cable to get it from a transmitter to an antenna with minimal loss.
In a leaky feeder, the outer shielding has deliberate gaps, slots, or a loose braided mesh.
- Transmitting: As the RF signal travels down the center conductor, a calculated amount of electromagnetic energy “leaks” out through these slots, providing a localized signal.
- Receiving: Conversely, when a portable radio transmits nearby, the signal leaks into the cable through the same slots and is carried back to the main base station.
Line amplifiers are typically placed at regular intervals along the cable run to boost the signal, counteracting the natural loss of energy as it leaks out over long distances.