Radome

Radomes at the Misawa Security Operations Center, Misawa, Japan.

A radome (a portmanteau word composed of the words radar and dome) is a weatherproof enclosure used to protect an antenna.

Purpose

It is used mainly to prevent ice, especially freezing rain, from accumulating directly onto the metal surface of the antenna. In the case of a spinning radar dish antenna, the radome also protects from debris and rotational irregularities due to wind. On aircraft, in addition to giving protection, the radome streamlines the antenna, thereby reducing drag.

For stationary antennas, excessive amounts of ice can de-tune the antenna to the point where its impedance at the input frequency rises drastically, causing VSWR to rise as well. This reflected power goes back to the transmitter, where it can cause overheating. A foldback circuit activates to prevent this; however, it causes the station's output power to drop dramatically, reducing its range.

One of the first radomes: the radome (top) covering the H2S radar system rotating antenna (bottom) on a Halifax bomber

A radome prevents this by covering the antenna's exposed parts with a sturdy, weatherproof material, typically fibreglass, which keeps the ice far enough away from the antenna to prevent any serious issues. A radome does however add to the wind load and the ice load, in addition to its own weight, and so must be planned for when considering overall structural load.

For this reason, and the fact that radomes may be unsightly if near the ground, heaters are often used instead. Usually running on DC, the heaters do not interfere physically or electrically with the AC of the radio transmission.

For radar dishes, the single, large, ball-shaped dome (usually geodesic) also protects the rotational mechanism, and the sensitive electronics, and is heated in colder climates to prevent icing.

The Menwith Hill spy base, which includes over 30 radomes, is widely believed to regularly intercept satellite communications. At Menwith Hill, the radome enclosures have a further use in preventing observers from deducing the direction of the antennae, and therefore which satellites are being targeted.

For maritime satellite communications service, radomes are widely used to protect dish antennas which are continually tracking fixed satellites while the ship's deck experiences pitch, roll and yaw movements. Large cruise ships and oil tankers may have radomes over 3 m in diameter to suit broadband transmissions for television, voice, data and internet. Small private yachts may use radomes as small as 26 cm for voice and low speed data.

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.