Radiating Coaxial Cable…
A wireless microphone installation may require the receiver to be installed in one area, while the transmitter is used in another. In such an application, remote mounting the antennas in the performance area is recommended for proper RF coverage. Choosing the correct antennas, cabling, and mounting scheme is essential for proper installation; Shure offers technical publications on this subject, such as: http://www.shure.com/publications/us_pro_antenna_setup_ea.pdf
But when the area being covered is an unusual shape, or if there are several areas, or if multiple floors of a building need to be covered with the same wireless system, radiating coaxial cable, or "leaky coax", can be considered as an alternative to traditional antennas.
Radiating coaxial cable is similar to the standard coax cable employed when mounting antennas remotely. Radiating coax has slots cut in the cable shield that allow RF to enter (or exit) the cable at any point along its length. Radiating coax is often used for distributed communication systems in tunnels, mines, and subway systems. The cable can be designed to handle any number of frequency ranges and can be installed in numerous ways. There are specialized mounting accessories and some cable designs are thin strips which can be mounted along ceiling tiles. Plenum-rated cable is also available.
For wireless microphone systems, radiating coax may be considered in situations where a standard antenna will not provide adequate coverage. This typical radiating cable will be thick, 0.5 to 2 inches in diameter, so it is best suited to permanent installations, e.g. a museum with several floors. A length of cable can be installed near the ceiling of each area that needs to be covered. Avoid placing radiating coax directly next to metal surfaces; it should be at least two inches away. Because the cable can potentially pick up more outside interference than standard coaxial cable, the transmitter should be within 40 feet (or less) of the radiating cable for best performance. A termination load must be used to prevent standing waves and/or an unacceptable amount of signal loss. If there is a need to cover an outdoor area as well, the radiating coax may be terminated with a 1/2 wave antenna.
Radiating coax is also useful for personal monitor systems (PSM). In this application, the PSM transmitter drives the radiating coax and the PSM receivers pick up the RF signal being radiated. When used as a transmitting antenna for PSM, radiating coax emits RF energy along its entire length, similar to a fluorescent lamp emitting light down the length of the glass tube.
Like standard coaxial cable, cable length and operating frequency directly affect the signal attenuation of radiating coax. In order to minimize signal loss, a larger diameter cable must be used for longer length runs or higher frequencies.
Recommended sources for radiating coaxial cable and its application, use, or installation:
Radio Frequency Systems (Radiaflex)