Radome

Last updated

Geodesic radomes at the Misawa Security Operations Center, Misawa, Japan Navy-Radome.jpg
Geodesic radomes at the Misawa Security Operations Center, Misawa, Japan
A Boeing E-3 Sentry, showing its rotodome mounted above the fuselage E3D Sentry - RIAT 2009 (3871588664).jpg
A Boeing E-3 Sentry, showing its rotodome mounted above the fuselage

A radome (which is a portmanteau of radar and dome) is a structural, weatherproof enclosure that protects a radar antenna. The radome is constructed of material that minimally attenuates the electromagnetic signal transmitted or received by the antenna, effectively 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.

A portmanteau or portmanteau word is a linguistic blend of words, in which parts of multiple words or their phones (sounds) are combined into a new word, as in smog, coined by blending smoke and fog, or motel, from motor and hotel. In linguistics, a portmanteau is defined as a single morph that represents two or more morphemes.

Radar object detection system based on radio waves

Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object(s). Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.

Dome architectural element that resembles the hollow upper half of a sphere

A dome is an architectural element that resembles the hollow upper half of a sphere. The precise definition has been a matter of controversy. There are also a wide variety of forms and specialized terms to describe them. A dome can rest upon a rotunda or drum, and can be supported by columns or piers that transition to the dome through squinches or pendentives. A lantern may cover an oculus and may itself have another dome.

Contents

Radomes can be constructed in several shapes — spherical, geodesic, planar, etc. — depending on the particular application, using various construction materials such as fiberglass, PTFE-coated fabric, and others.

Geodesic dome spherical shell structure based on a network of great circles on the surface of a sphere

A geodesic dome is a hemispherical thin-shell structure (lattice-shell) based on a geodesic polyhedron. The triangular elements of the dome are structurally rigid and distribute the structural stress throughout the structure, making geodesic domes able to withstand very heavy loads for their size.

Fiberglass (US) or fibreglass (UK) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet, or woven into a fabric. The plastic matrix may be a thermoset polymer matrix—most often based on thermosetting polymers such as epoxy, polyester resin, or vinylester—or a thermoplastic.

Polytetrafluoroethylene polymer

Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best-known brand name of PTFE-based formulas is Teflon by Chemours. Chemours is a spin-off of DuPont, which originally discovered the compound in 1938. Another popular brand name of PTFE is Syncolon® by Synco Chemical Corporation.

When found on fixed-wing aircraft with forward-looking radar, as are commonly used for object or weather detection, [1] the nose cones often additionally serve as radomes. On aircraft used for airborne early warning and control (AEW&C), a rotating radome, often called a "rotodome", is mounted on the top of the fuselage for 360-degree coverage. Some newer AEW&C configurations instead use three antenna modules inside a radome, usually mounted on top of the fuselage, for 360-degree coverage, such as the Chinese KJ-2000 and Indian DRDO AEW&Cs.

Aircraft machine that is able to fly by gaining support from the air other than the reactions of the air against the earth’s surface

An aircraft is a machine that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. Common examples of aircraft include airplanes, helicopters, airships, gliders, and hot air balloons.

Nose cone Foremost tip of aircraft, rockets, and missiles

A nose cone is the forwardmost section of a rocket, guided missile or aircraft. The cone is shaped to offer minimum aerodynamic drag. Nose cones are also designed for travel in and under water and in high-speed land vehicles.

Airborne early warning and control Airborne system of surveillance radar plus command and control functions

An airborne early warning and control (AEW&C) system is an airborne radar picket system designed to detect aircraft, ships and vehicles at long ranges and perform command and control of the battlespace in an air engagement by directing fighter and attack aircraft strikes. AEW&C units are also used to carry out surveillance, including over ground targets and frequently perform C2BM functions similar to an Air Traffic Controller given military command over other forces. When used at altitude, the radar on the aircraft allows the operators to detect and track targets and distinguish between friendly and hostile aircraft much farther away than a similar ground-based radar. Like a ground-based radar, it can be detected by opposing forces, but because of its mobility, it is much less vulnerable to counter-attack.

On rotary-wing and fixed-wing aircraft using microwave satellite for beyond-line-of-sight communication, radomes often appear as blisters on the fuselage. [2] In addition to protection, radomes also streamline the antenna system, thus reducing drag.

In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity. Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.

Use

One of the first radomes. The radome (top) covers the H2S radar system rotating antenna (bottom) on a Halifax bomber H2S Radome And Scanner On Halifax.jpg
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.

Freezing rain is the name given to rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow, ice pellets, or hail, freezing rain is made entirely of liquid droplets. The raindrops become supercooled while passing through a sub-freezing layer of air hundreds of meters above the ground, and then freeze upon impact with any surface they encounter, including the ground, trees, electrical wires, aircraft, and automobiles. The resulting ice, called glaze ice, can accumulate to a thickness of several centimeters and cover all exposed surfaces. The METAR code for freezing rain is FZRA.

Parabolic antenna type of antenna

A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct the radio waves in a narrow beam, or receive radio waves from one particular direction only. Parabolic antennas have some of the highest gains, meaning that they can produce the narrowest beamwidths, of any antenna type. In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the wavelength of the radio waves used, so parabolic antennas are used in the high frequency part of the radio spectrum, at UHF and microwave (SHF) frequencies, at which the wavelengths are small enough that conveniently-sized reflectors can be used.

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 foldback circuit 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. [3] 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.

Tuner (radio) frequency selection subsystem for a radio receiver

A tuner is a subsystem that receives radio frequency (RF) transmissions like radio broadcasts and converts the selected carrier frequency and its associated bandwidth into a fixed frequency that is suitable for further processing, usually because a lower frequency is used on the output. Broadcast FM/AM transmissions usually feed this intermediate frequency (IF) directly into a demodulator that convert the radio signal into audio-frequency signals that can be fed into an amplifier to drive a loudspeaker.

Electrical impedance intensive physical property

Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably.

Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

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 sensitive electronics, 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 15 m (50 ft) 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 46 m (150 ft), and a height of 26 m (84 ft). This radome consisted of 590 panels, and was designed for winds up to 240 km/h (150 mph). The total radome weight was 92,700 kg (204,400 lb) with a surface area of 3,680 m2 (39,600 sq ft). 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.

Maritime satellites

A yacht fitted with small KNS tracking dishes for SES Broadband for Maritime, protected by radomes KNS radomes.jpg
A yacht fitted with small KNS tracking dishes for SES Broadband for Maritime, protected by radomes

For maritime satellite 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 3 m 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 85 cm motorised dish used in the SES Broadband for Maritime system. Small private yachts may use radomes as small as 26 cm 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. An example of this is the "pyramid" which replaced the "tourist attraction" golfball-style radome installations at RAF Fylingdales.

Notes

  1. example of dented radome
  2. example of helicopter radome
  3. Gordon, J.E., The New Science of Strong Materials: 2nd Edition, Pelican, 1976.

Related Research Articles

Kamov Ka-25 naval helicopter

The Kamov Ka-25 was a naval helicopter, developed for the Soviet Navy in the USSR from 1958.

Boeing 737 AEW&C Airborne early warning and control aircraft

The Boeing 737 AEW&C is a twin-engine airborne early warning and control aircraft. It is lighter than the 707-based Boeing E-3 Sentry, and mounts a fixed, active electronically scanned array radar antenna instead of a rotating one. It was designed for the Royal Australian Air Force (RAAF) under "Project Wedgetail" and designated E-7A Wedgetail.

Clear Air Force Station

Clear Air Force Station is a United States Air Force Station radar station for detecting incoming ICBMs and submarine-launched ballistic missiles to NORAD's command center and to provide Space Surveillance data to Air Force Space Command's Space Control Center (SCC). Clear's AN/FPS-123 Upgraded Early Warning Radar is part of the Solid State Phased Array Radar System (SSPARS) which also includes those at Beale AFB, Cape Cod AFS, RAF Fylingdales and Thule Site J. The "historic property" was one of the Alaska World War II Army Airfields and later a Cold War BMEWS site providing NORAD data to Colorado's BMEWS Central Computer and Display Facility (CC&DF).

Haystack Observatory American observatory affiliated with MIT

Haystack Observatory is an astronomical observatory owned by Massachusetts Institute of Technology (MIT). It is located in Westford, Massachusetts (US), approximately 45 kilometers (28 mi) northwest of Boston. Haystack was initially built by MIT's Lincoln Laboratory for the United States Air Force and was known as Haystack Microwave Research Facility. Construction began in 1960, and the antenna began operating in 1964. In 1970 the facility was transferred to MIT, which then formed the Northeast Radio Observatory Corporation (NEROC) with a number of other universities to operate the site as the Haystack Observatory. As of January 2012, a total of nine institutions participated in NEROC.

The AN/APG-76 radar is a pulse Doppler Ku band multi-mode radar; manufactured by Northrop Grumman, and it is a member of a radar family produced by Norden based on the similar design principles and evolution.

Mount Hebo Air Force Station

Mount Hebo Air Force Station is a closed United States Air Force General Surveillance Radar station. It is located 5.2 miles (8.4 km) east-southeast of Hebo, Oregon, located at the top of 3,154-foot (961 m) Mount Hebo. It was closed in 1980.

689th Radar Squadron

The 689th Radar Squadron is an inactive United States Air Force unit. It was last assigned to the 25th Air Division, stationed at Mount Hebo Air Force Station, Oregon. It was inactivated on 30 June 1979.

Advanced Enclosed Mast/Sensor

The US Navy's Advanced Enclosed Mast/Sensor (AEM/S) system fully integrates advanced materials, structures, and manufacturing technologies with sensor technology, electromagnetics, and signature reduction.

The AN/APS-2, originally known as ASG, was a surface search radar developed by Philco originally for use in US Coast Guard blimps to detect German submarines. It proved better than several similar models then being built, and was ordered by the RAF Coastal Command where it was known as ASV Mark V. It was used primarily on British Liberator GR bombers, where they were instrumental in closing the Mid-Atlantic Gap and the subsequent destruction of the German U-boat fleet in May/June 1943.

KJ-2000 Airborne early warning and control aircraft

KJ-2000, NATO reporting name: Mainring is a Chinese Airborne early warning and control system comprising domestically designed electronics and radars installed on a modified Ilyushin Il-76 airframe.

The Tracking & Imaging Radar (TIRA) system serves as the central experimental facility for the development and investigation of radar techniques for the detection and reconnaissance of objects in space, and to a certain degree also of air targets. TIRA has a 34-metre parabolic dish antenna is a monopulse radar operating at 1.333 GHz or 22.5 cm and 16.7 GHz or 1.8 cm wavelengths. The L-band is usually used for tracking debris with a 0.45° beam width, at 1 MW peak power. The system is capable of determining orbits from direction angles, range and Doppler shift for single targets. The detection size threshold is about 2 cm at 1000 km range. The radar conducts regular ‘beam park’ experiments, where the radar beam is pointed in a fixed direction on the celestial sphere for 24 hours, scanning 360° in a narrow strip a complete Earth rotation. The tracking sensitive can be enhanced when the TIRA system is used as a transmitter, part of a bistatic radar system. In conjunction with the Effelsberg Radio Telescope, functioning as a receiver, the combined system has a detection size threshold of 1 cm. The Ku-band is used for imaging in Inverse Synthetic Aperture Radar (ISAR) mode, with 13 kW peak power, the radar is capable of producing images with range resolutions better than 7 cm. The dish can be turned full 360° in azimuth with speed of 24° per second and 90° in elevation. The radar is protected by a radome with 47 meters diameter – one of the largest in the world.

IAI EL/W-2085 Airborne early warning system

The IAI EL/W-2085 is an airborne early warning and control (AEW&C) multi-band radar system developed by Israel Aerospace Industries (IAI) and Elta Electronics Industries of Israel. Its primary objective is to provide intelligence to maintain air superiority and conduct surveillance. The system is currently in-service with Israel and Singapore, and in the future Italy and the United States.

The Avco AN/FPS-26 Radar was an Air Defense Command height finder radar developed in the Frequency Diversity Program with a tunable 3-cavity power klystron for electronic counter-countermeasures (e.g. to counter jamming). Accepted by the Rome Air Development Center on 20 January 1960 for use at SAGE radar stations, the AN/FPS-26 processed height-finder requests (e.g., from Air Defense Direction Centers) by positioning to the azimuth of a target aircraft using a high-pressure hydraulic drive, then "nodding" in either a default automatic mode or by operator command. The inflatable radome required a minimum pressure to prevent contact with the antenna which would result in damage to both (technicians accessed the antenna deck via an air lock.) To maintain high dielectric strength, the waveguide was pressurized with sulfur hexafluoride (SF6), which technicians were warned would produce deadly fluorine if the waveguide arcing occurred.

Fairey Gannet AEW.3 British airborne early warning aircraft

The Fairey Gannet AEW.3 is a variant of the Fairey Gannet anti-submarine warfare aircraft intended to be used in the airborne early warning (AEW) role on aircraft carriers of the Royal Navy. It was introduced to service in 1959 to replace the obsolete Douglas Skyraider, and was intended as an interim solution until the planned introduction of a new, purpose built AEW platform for use on the planned CVA-01 aircraft carriers. Neither the new aircraft carriers nor the new AEW aircraft were proceeded with, and the Gannet AEW.3 remained in service until the last aircraft carrier that could operate it was retired in 1978.

Hawker Siddeley P.139B

The Hawker Siddeley P.139B was a proposed airborne early warning aircraft intended to operate from aircraft carriers of the Royal Navy. The P.139B formed part of the a major equipment procurement plan for the RN in the 1960s intended to give the service a force of new, modern carriers capable of operating air groups consisting of equally modern aircraft. However, cuts in defence spending by the British Government in the mid-1960s meant that these proposals never came to fruition.

An Arctic Tower is a 20 ft diameter cylindrical radar station structure of the AN/GPA-33 Radar Set Group for protecting a USAF radar's antenna and electronic cabinets. Designed for low temperatures and strong winds, the 25 ft high tower's top platform supported an antenna group and a 20 ft high CW-313/FPS radome which was "capable of withstanding two inches of ice" and winds of 109 knots. The 25,000 lb Arctic Tower was designed for supporting Radar Set AN//TPS-10D (AN/FPS-4) or Radar Set AN/TPS-1D, and could support other systems up to a load of 100psf on the 20 foot diameter platform, the interior 2nd floor, or the ground floor. In addition to protecting a radar system, the tower housed other AN/GPA-33 equipment such as the Radome Interior Control Group (OA-709/GPA-33) which included

Beriev A-100 Airborne early warning and control aircraft

The Beriev A-100 is a Russian-built airborne early warning and control (AEW&C) aircraft based on the Il-76MD-90A transport aircraft. This aircraft is developed to replace the Beriev A-50 in Russian Air Force service. Avionics and configuration will be similar to the A-50U, but with a new Vega Premier Active Phased Array Radar.

Radar tower

A radar tower is a tower whose function is to support a radar facility, usually a local airport surveillance radar, and hence often at or in the vicinity of an airport or a military air base. In addition, radar towers are used for the installation and operation of search and height finder radars at military radar stations where the mission is to support air defense missions. These missions were characterized as Aircraft Control & Warning (AC&W) or Long Range Surveillance in support of the Semi-automatic Ground Environment (SAGE).