A radome (a portmanteau of radar and dome) is a structural, weatherproof enclosure that protects a radar antenna.[1] The radome is constructed of material transparent to radio waves. Radomes protect the antenna from weather and conceal antenna electronic equipment from view. They also protect nearby personnel from being accidentally struck by quickly rotating antennas.
Radomes can be constructed in several shapes– spherical, geodesic, planar, etc.– depending on the particular application, using various construction materials such as fiberglass, polytetrafluoroethylene (PTFE)-coated fabric, and others.[2]
In addition to radar protection, radomes on aircraft platforms also act as fairings that streamline the antenna system, thus reducing drag. When found on fixed-wing aircraft with forward-looking radar, as are commonly used for object or weather detection, the nose cones often additionally serve as radomes. On airborne early warning and control (AEW&C) aircraft (e.g. the American E-3 Sentry), a discus-shaped rotating radome, often called a "rotodome", is mounted on the top of the fuselage for 360-degree scanning coverage. Some newer AEW&C configurations instead use three 120-degree phased array modules inside a stationary radome, examples being the Chinese KJ-2000 and Indian DRDO AEW&Cs. On fixed-wing and rotary-wing aircraft using microwavesatellite for beyond-line-of-sight communication, radomes often appear as bulged "blisters" on the fuselage.[3]
The air supported radome built by Walter Bird in 1948 at the Cornell Aeronautical Laboratory is the first pneumatic construction built in history.[4][2]
Use
One of the first radomes. The radome (top) covers the H2S radar system rotating antenna (bottom) on a Halifax bomber
A radome is often used to prevent ice and freezing rain from accumulating on antennas. In the case of a spinning radar parabolic antenna, the radome also protects the antenna from debris and rotational irregularities due to wind. Its shape is easily identified by its hardshell, which has strong properties against being damaged.
Stationary antennas
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 the voltage standing wave ratio (VSWR) to rise as well. This reflected power goes back to the transmitter, where it can cause overheating. A foldbackcircuit can act to prevent this; however, one drawback of its use is that it causes the station's output power to drop dramatically, reducing its range. A radome avoids that by covering the antenna's exposed parts with a sturdy, weatherproof material, typically fiberglass, keeping debris or ice away from the antenna, thus preventing any serious issues. One of the main driving forces behind the development of fiberglass as a structural material was the need during World War II for radomes.[5] When considering structural load, the use of a radome greatly reduces wind load in both normal and iced conditions. Many tower sites require or prefer the use of radomes for wind loading benefits and for protection from falling ice or debris.
Where radomes might be considered unsightly if near the ground, electric antenna heaters could be used instead. Usually running on direct current, the heaters do not interfere physically or electrically with the alternating current of the radio transmission.
Radar dishes
For radar dishes, a single, large, ball-shaped dome also protects the rotational mechanism and the sensitiveelectronics, and is heated in colder climates to prevent icing.
The RAF Menwith Hill electronic surveillance base, which includes over 30 radomes, is widely believed to regularly intercept satellite communications. At Menwith Hill, the radome enclosures prevent observers from seeing the direction of the antennas, and therefore which satellites are being targeted. Similarly, radomes prevent observation of antennas used in ECHELON facilities.
The United States Air Force Aerospace Defense Command operated and maintained dozens of air defense radar stations in the contiguous United States and Alaska during the Cold War. Most of the radars used at these ground stations were protected by rigid or inflatable radomes. The radomes were typically at least 15m (50ft) in diameter and the radomes were attached to standardized radar tower buildings that housed the radar transmitter, receiver and antenna. Some of these radomes were very large. The CW-620 was a space frame rigid radome with a maximum diameter of 46m (150ft), and a height of 26m (84ft). This radome consisted of 590 panels, and was designed for winds up to 240km/h (150mph). The total radome weight was 92,700kg (204,400lb) with a surface area of 3,680m2 (39,600sqft). The CW-620 radome was designed and constructed by Sperry-Rand Corporation for the Columbus Division of North American Aviation. This radome was originally used for the FPS-35 search radar at Baker Air Force Station, Oregon. When Baker AFS was closed the radome was moved to provide a high-school gymnasium in Payette, Idaho. Pictures and documents are available online at radomes.org/museum for Baker AFS/821st Radar Squadron.
For maritimesatellite communications service, radomes are widely used to protect dish antennas which are continually tracking fixed satellites while the ship experiences pitch, roll and yaw movements. Large cruise ships and oil tankers may have radomes over 3m in diameter covering antennas for broadband transmissions for television, voice, data, and the Internet, while recent developments allow similar services from smaller installations such as the 85cm motorised dish used in the SES Broadband for Maritime system. Small private yachts may use radomes as small as 26cm in diameter for voice and low-speed data.
Alternatives
An active electronically scanned array radar has no moving antenna and so a radome is not necessary.[2] An example of this is the pyramid which replaced the golfball-style radome installations at RAF Fylingdales.
Notes
↑ Wragg, David W. (1973). A Dictionary of Aviation (firsted.). Osprey. p.220. ISBN9780850451634.
Fiberglass or fibreglass is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth. The plastic matrix may be a thermoset polymer matrix—most often based on thermosetting polymers such as epoxy, polyester resin, or vinyl ester resin—or a thermoplastic.
An airborne early warning and control (AEW&C) system is an airborne radar early warning system designed to detect aircraft, ships, vehicles, missiles and other incoming projectiles at long ranges, as well as performing command and control of the battlespace in aerial engagements by informing and directing friendly fighter and attack aircraft. AEW&C units are also used to carry out aerial surveillance over ground and maritime targets, and frequently perform battle management command and control (BMC2). When used at altitude, the radar system on AEW&C aircraft allows the operators to detect, track and prioritize targets and identify friendly aircraft from hostile ones in real-time and from much farther away than ground-based radars. Like ground-based radars, AEW&C systems can be detected and targeted by opposing forces, but due to aircraft mobility and extended sensor range, they are much less vulnerable to counter-attacks than ground systems.
Radar cross-section (RCS), denoted σ, also called radar signature, is a measure of how detectable an object is by radar. A larger RCS indicates that an object is more easily detected.
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The N-Class, or as popularly known, the "Nan ship", was a line of non-rigid airships built by the Goodyear Aircraft Company of Akron, Ohio for the US Navy. This line of airships was developed through many versions and assigned various designators as the airship designation system changed in the post World War II era. These versions included airships configured for both anti-submarine warfare and airborne early warning (AEW) missions.
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The KJ-2000 is a Chinese second-generation airborne early warning and control (AEW&C) aircraft developed by the Shaanxi Aircraft Corporation, and is the first AEW&C system in service to the People's Liberation Army Air Force. It is built upon a modified Russian Ilyushin Il-76 airframe using domestically designed avionics and a fixed radome featuring three active electronically scanned array (AESA) radars each covering a 120-degree sector, unlike the rotating radome on the comparable E-3 Sentry serving the United States Air Force.
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The Saugatuck Gap Filler Annex is a decommissioned air defense radar installation previously of the United States Air Force. It served in the vast Cold War era Semi-Automatic Ground Environment (SAGE) air defense system. Of the hundreds of SAGE radars, Saugatuck's is one of, perhaps, two that remain nearly completely intact.
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