A leaky feeder is a coaxial cable that has small sections of its copper shielding stripped away to allow radio frequency (RF) signals to escape. Leaky feeders, which act as extended antennas, are also called radiating cables.
Leaky feeders are used in places where the actual structure makes RF communication difficult. Leaky feeders are often used in structures with metal frameworks such as skyscrapers, tunnels, ships and planes to extend mobile coverage. They are also useful in situations where low power levels are required to prevent interference with wireless microphones or other communication technologies that share the same frequency spectrum.
Leaky feeders were originally used in underground mines. Normally it would be impossible for someone in a mine to communicate with the surface with a hand-held radio. Sufficient cabling working in conjunction with signal amplifiers, however, can be strong enough to cover an entire mine. Base stations on the surface can then route and combine multiple audio channels so the miner’s communications to can remain separate or be combined as needs require.
This video from Minecom explains how leaky feeders are used for underground communication.