Radio spectrum

bandradio bandspectrum
Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on bands not used for other purposes. Most radar bands are in the microwave part of the spectrum, although certain important applications for meteorology make use of powerful transmitters in the UHF band. Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, or include waves of any lower frequency.

Dowding system

Air Defence systemcommand and control system
It used a widespread dedicated land-line telephone network to rapidly collect information from Chain Home (CH) radar stations and the Royal Observer Corps (ROC) in order to build a single image of the entire UK airspace and then direct defensive interceptor aircraft and anti-aircraft artillery against enemy targets. The system was built by the Royal Air Force just before the start of World War II, and proved decisive in the Battle of Britain. The Dowding system was developed after tests demonstrated problems relaying information to the fighters before it was out of date.

Space surveillance

Space surveillance and trackingtracking
Preventing a returning space object, which to radar looks like a missile, from triggering a false alarm in missile-attack warning sensors. Charting the present position of space objects and plot their anticipated orbital paths. Detecting new man-made objects in space. Producing a running catalogue of man-made space objects. Determining which country owns a re-entering space object. Informing countries whether or not objects may interfere with satellites and International Space Station orbits. Providing data for future anti-satellite weapons systems.

Tizard Mission

British mission, led by TizardSir Henry TizardTizard delegation
At a meeting hosted by NDRC's two-month-old "Microwave Committee" chairman Dr Alfred Loomis at the Wardman Park Hotel on 19 September 1940 the British disclosed the technical details of the Chain Home early warning radar stations. The British thought the Americans did not have anything like this, but found it was virtually identical to the US Navy's longwave CXAM radar. The Americans then described their microwave research done by Loomis and Karl Compton earlier in 1940. The British realised that Bell Telephone Laboratories and General Electric both could contribute a lot to receiver technology.

Terrain-following radar

terrain following radarterrain-followingTerrain Following
The use of terrain-following radar is therefore a compromise between the increased survivability due to terrain-masking and the ease with which the aircraft can be targeted if it is seen. Since the radar cannot tell what is beyond any immediate terrain, the flight path may suffer from "ballooning" over the top of high ground. Furthermore, small obstacles such as radio antennas and electricity pylons may not show up on the radar at all. The objects present collision hazards when flying at very low level. Even an automated system has limitations, and all aircraft with terrain-following radars installed have limits on how low and fast they can fly.

Massachusetts Institute of Technology

MITMassachusetts Institute of Technology (MIT)M.I.T.
In electronics, magnetic core memory, radar, single electron transistors, and inertial guidance controls were invented or substantially developed by MIT researchers. Harold Eugene Edgerton was a pioneer in high speed photography and sonar. Claude E. Shannon developed much of modern information theory and discovered the application of Boolean logic to digital circuit design theory. In the domain of computer science, MIT faculty and researchers made fundamental contributions to cybernetics, artificial intelligence, computer languages, machine learning, robotics, and cryptography.

SS Normandie

NormandieSS ''NormandieS.S. ''Normandie
An early form of radar was installed to prevent collisions. The rudder frame, including the 125-ton cast steel connecting rod, was produced by Škoda Works in Czechoslovakia. The luxurious interiors were designed in Art Déco and Streamline Moderne style. Many sculptures and wall paintings made allusions to Normandy, the province of France for which Normandie was named. Drawings and photographs show a series of vast public rooms of great elegance. Normandie's voluminous interior spaces were made possible by having the funnel intakes split to pass along the sides of the ship, rather than straight upward. French architect Roger-Henri Expert was in charge of the overall decorative scheme.


laserslaser beamlaser light
Gould's notes included possible applications for a laser, such as spectrometry, interferometry, radar, and nuclear fusion. He continued developing the idea, and filed a patent application in April 1959. The U.S. Patent Office denied his application, and awarded a patent to Bell Labs, in 1960. That provoked a twenty-eight-year lawsuit, featuring scientific prestige and money as the stakes. Gould won his first minor patent in 1977, yet it was not until 1987 that he won the first significant patent lawsuit victory, when a Federal judge ordered the U.S. Patent Office to issue patents to Gould for the optically pumped and the gas discharge laser devices.

Pathfinder (RAF)

PathfinderPathfinder ForcePathfinders
In the era before the widespread use of radar and the techniques needed to guide fighters to their targets with radar, night bombing would render the bombers vulnerable only if they were picked up by searchlights, a relatively rare occurrence. Offsetting the advantages of night bombing was the understanding that identifying the targets and attacking them accurately would be much more difficult. This meant a night bomber force was only useful against very large targets, like cities, and was one of the reasons daylight bombing was considered.


searchlightssearch lightspotlight
Although searchlights remained in use throughout the war, the newly developed radar proved to be a far more effective locating device, and Japanese radar development lagged far behind that of the US. Searchlights were first used in the First World War to create "artificial moonlight" to enhance opportunities for night attacks by reflecting searchlight beams off the bottoms of clouds, a practice which continued in the Second World War. The term "artificial moonlight" was used to distinguish illumination provided by searchlights from that provided by natural moonlight, which was referred to as "movement light" in night-time manoeuvers.


armed forcesdefensedefence
During the war, significant advances were made in military communications through increased use of radio, military intelligence through use of the radar, and in military medicine through use of penicillin, while in the air, the guided missile, jet aircraft, and helicopters were seen for the first time. Perhaps the most infamous of all military technologies was the creation of the atomic bomb, although the exact effects of its radiation were unknown until the early 1950s. Far greater use of military vehicles had finally eliminated the cavalry from the military force structure.

Side looking airborne radar

side-looking airborne radarside-looking radarSLAR
Synthetic aperture radar refers to a method for improving the azimuth resolution (not range resolution). * Radar imaging \tau = duration of the (may be compressed in matched receiver) radar pulse. c_0 = speed of light. \gamma = depression angle. \lambda = wavelength. L = antenna length (in direction of flight). \rho = slant range. H = height of the platform. Radartutorial. "A Sideways Glance" a 1966 Flight article on SLAR.

United States Naval Research Laboratory

Naval Research LaboratoryNRLU.S. Naval Research Laboratory
The same polymer films are used in Los Angeles-class submarine radomes to repel water and enable radar operation soon after surfacing. Scientists at NRL frequently contribute theoretical and experimental research on novel materials, particularly magnetic materials and nanomaterials and thermoplastic. The first modern U.S. radar was invented and developed at NRL in Washington, DC in 1922. By 1939, NRL installed the first operational radar aboard the USS New York, in time for radar to contribute to naval victories of the Coral Sea, Midway and Guadalcanal. NRL then further developed over-the-horizon radar as well as radar data displays.


heavier-than-airflying machineheavier-than-air flight
The avionics comprise the flight control systems and related equipment, including the cockpit instrumentation, navigation, radar, monitoring, and communication systems. The flight envelope of an aircraft refers to its capabilities in terms of airspeed and load factor or altitude. The term can also refer to other measurements such as maneuverability. When a craft is pushed, for instance by diving it at high speeds, it is said to be flown outside the envelope, something considered unsafe. The range is the distance an aircraft can fly between takeoff and landing, as limited by the time it can remain airborne.

Vessel traffic service

VTSmaritime vessel traffic controlVessel Traffic Control System
Typical VTS systems use radar, closed-circuit television (CCTV), VHF radiotelephony and automatic identification system to keep track of vessel movements and provide navigational safety in a limited geographical area. The VTS guidelines (see VTS Manual IALA, Edition 6, Chapter 12, for general reference) require that the VTS authority should be provided with sufficient staff, appropriately qualified, suitably trained and capable of performing the tasks required, taking into consideration the type and level of services to be provided in conformity with the current IMO guidelines on the subject.

Radar cross-section

radar cross sectionradar signatureRCS
All other factors being equal, the plane will have a stronger signal from the side than from the front so the orientation between the Radar station and the target is important. The relief of a surface could contain indentations that act as corner reflectors which would increase RCS from many orientations. This could arise from open bomb-bays, engine intakes, ordnance pylons, joints between constructed sections, etc. Also, it can be impractical to coat these surfaces with radar-absorbent materials. The size of a target's image on radar is measured by the radar cross section or RCS, often represented by the symbol σ and expressed in square meters. This does not equal geometric area.

Stealth technology

Dielectric composites are more transparent to radar, whereas electrically conductive materials such as metals and carbon fibers reflect electromagnetic energy incident on the material's surface. Composites may also contain ferrites to optimize the dielectric and magnetic properties of a material for its application. Radar-absorbent material (RAM), often as paints, are used especially on the edges of metal surfaces. While the material and thickness of RAM coatings can vary, the way they work is the same: absorb radiated energy from a ground or air based radar station into the coating and convert it to heat rather than reflect it back.

Reflection (physics)

Reflection of VHF and higher frequencies is important for radio transmission and for radar. Even hard X-rays and gamma rays can be reflected at shallow angles with special "grazing" mirrors. Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface. In specular reflection the phase of the reflected waves depends on the choice of the origin of coordinates, but the relative phase between s and p (TE and TM) polarizations is fixed by the properties of the media and of the interface between them.

Electronic countermeasure

ECMelectronic countermeasureselectronic attack
Basic radar ECM strategies are (1) radar interference, (2) target modifications, and (3) changing the electrical properties of air. Interference techniques include jamming and deception. Jamming is accomplished by a friendly platform transmitting signals on the radar frequency to produce a noise level sufficient to hide echos. The jammer's continuous transmissions will provide a clear direction to the enemy radar, but no range information. Deception may use a transponder to mimic the radar echo with a delay to indicate incorrect range. Transponders may alternatively increase return echo strength to make a small decoy appear to be a larger target.

Bawdsey Manor

Air Ministry Research Establishment
From 1937 Bawdsey was operational as the first of the RDF (radar) Chain Home, and during World War 2 also acquired Chain Home Low and Coast Defence/Centimetric equipment for tracking enemy ships. It continued as a radar station through most of the Cold War. Demolition of the 10 towers began in the 1960s, and all are now gone. Bawdsey Manor continued as an RAF base through the Cold War and Bloodhound Missiles were sited on the cliffs until the Bloodhound force ceased operations in 1990, when all the missiles were withdrawn to RAF West Raynham. RAF Bawdsey was closed in 1991.

Active radar homing

active radar seekerARHactive radar
Active radar homing (ARH) is a missile guidance method in which a missile contains a radar transceiver (in contrast to semi-active radar homing, which uses only a receiver) and the electronics necessary for it to find and track its target autonomously. NATO brevity code for an air-to-air active radar homing missile launch is Fox Three. There are two major advantages to active radar homing: Many missiles employing this type of guidance have an extra trick up their sleeves; If the target does attempt to use noise jamming, they can in effect turn into an anti-radiation missile and home in on the target's radiation passively (home-on-jam).

Chaff (countermeasure)

chaffWindowchaff rocket launchers
For over a year the curious situation arose where both sides of the conflict knew how to use chaff to jam the other side's radar but had refrained from doing for fear of their opponent replying in kind. Window rendered the ground-controlled Himmelbett (canopy bed) fighters of the Kammhuber Line unable to track their targets in the night sky and the early UHF-band versions of the airborne intercept Lichtenstein radar (following the capture of a Ju 88R-1 night fighter by the British in May 1943) useless, blinding radar-guided guns and spotlights dependent on the ground-based radar.


It made possible long distance telephone lines, public address systems, radio broadcasting, talking motion pictures, practical audio recording, radar, television, and the first computers. For 50 years virtually all consumer electronic devices used vacuum tubes. Early tube amplifiers often had positive feedback (regeneration), which could increase gain but also make the amplifier unstable and prone to oscillation. Much of the mathematical theory of amplifiers was developed at Bell Telephone Laboratories during the 1920s to 1940s.


GermanGerman NavyNavy
The Kriegsmarine also manned the Seetakt sea radars on the coasts. At the beginning of World War II, on 1 September 1939, the Marine Stoßtrupp Kompanie (Marine Attack Troop Company) landed in Danzig from the old battleship for conquering a Polish bastion. A reinforced platoon of the Marine Stoßtrupp Kompanie landed with soldiers of the German Army from destroyers on 9 April 1940 in Narvik. In June 1940 the Marine Stoßtrupp Abteilung (Marine Attack Troop Battalion) was flown in from France to the Channel Islands to occupy this British territory.