Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
The Battle of the Beams was a period early in the Second World War when bombers of the German Air Force (Luftwaffe) used a number of increasingly accurate systems of radio navigation for night bombing in the United Kingdom. British scientific intelligence at the Air Ministry fought back with a variety of their own increasingly effective means, involving jamming and deception signals. The period ended when the Wehrmacht moved their forces to the East in May 1941, in preparation for the attack on the Soviet Union.
Chain Home, or CH for short, was the codename for the ring of coastal early warning radar stations built by the Royal Air Force (RAF) before and during the Second World War to detect and track aircraft. Initially known as RDF, and given the official name Air Ministry Experimental Station Type 1 in 1940, the radar units were also known as Chain Home for most of their life. Chain Home was the first early warning radar network in the world and the first military radar system to reach operational status. Its effect on the war made it one of the most powerful weapons of what became known as the "Wizard War".
Direction finding (DF), or radio direction finding (RDF), is – in accordance with International Telecommunication Union (ITU) – defined as radio location that uses the reception of radio waves to determine the direction in which a radio station or an object is located. This can refer to radio or other forms of wireless communication, including radar signals detection and monitoring (ELINT/ESM). By combining the direction information from two or more suitably spaced receivers, the source of a transmission may be located via triangulation. Radio direction finding is used in the navigation of ships and aircraft, to locate emergency transmitters for search and rescue, for tracking wildlife, and to locate illegal or interfering transmitters. RDF was important in combating German threats during both the World War II Battle of Britain and the long running Battle of the Atlantic. In the former, the Air Ministry also used RDF to locate its own fighter groups and vector them to detected German raids.
The low-UHF band Würzburg radar was the primary ground-based tracking radar for the Wehrmacht's Luftwaffe and Kriegsmarine during World War II. Initial development took place before the war and the apparatus entered service in 1940. Eventually, over 4,000 Würzburgs of various models were produced. It took its name from the city of Würzburg.
Gee-H, sometimes written G-H or GEE-H, was a radio navigation system developed by Britain during World War II to aid RAF Bomber Command. The name refers to the system's use of the earlier Gee equipment, as well as its use of the "H principle" or "twin-range principle" of location determination. Its official name was AMES Type 100.
Serrate was a World War II Allied radar detection and homing device used by night fighters to track Luftwaffe night fighters equipped with the earlier UHF-band BC and C-1 versions of the Lichtenstein radar. It allowed RAF night fighters to attack their German counterparts, disrupting their attempts to attack the RAF's bomber force.
The SCR-268 was the United States Army's first radar system. Introduced in 1940, it was developed to provide accurate aiming information for antiaircraft artillery and was also used for gun laying systems and directing searchlights against aircraft. The radar was widely utilized by both Army and Marine Corps air defense and early warning units during World War II. By the end of World War II the system was already considered out of date, having been replaced by the much smaller and more accurate SCR-584 microwave-based system.
Conical scanning is a system used in early radar units to improve their accuracy, as well as making it easier to steer the antenna properly to point at a target. Conical scanning is similar in concept to the earlier lobe switching concept used on some of the earliest radars, and many examples of lobe switching sets were modified in the field to conical scanning during World War II, notably the German Würzburg radar. Antenna guidance can be made entirely automatic, as in the American SCR-584. Potential failure modes and susceptibility to deception jamming led to the replacement of conical scan systems with monopulse radar sets. They are still used by the Deep Space Network for maintaining communications links to space probes. The spin-stabilized Pioneer 10 and Pioneer 11 probes used onboard conical scanning maneuvers to track Earth in its orbit.
Monopulse radar is a radar system that uses additional encoding of the radio signal to provide accurate directional information. The name refers to its ability to extract range and direction from a single signal pulse.
A radar display is an electronic device that presents radar data to the operator. The radar system transmits pulses or continuous waves of electromagnetic radiation, a small portion of which backscatter off targets and return to the radar system. The receiver converts all received electromagnetic radiation into a continuous electronic analog signal of varying voltage that can be converted then to a screen display.
In radar systems, the blip-to-scan ratio, or blip/scan, is the ratio of the number of times a target appears on a radar display to the number of times it theoretically could be displayed. Alternately it can be defined as the ratio of the number of scans in which an accurate return is received to the total number of scans.
Radar, Airborne Interception, Mark VIII, or AI Mk. VIII for short, was the first operational microwave-frequency air-to-air radar. It was used by Royal Air Force night fighters from late 1941 until the end of World War II. The basic concept, using a moving parabolic antenna to search for targets and track them accurately, remained in use by most airborne radars well into the 1980s.
Radar, Gun Laying, Mark I, or GL Mk. I for short, was an early radar system developed by the British Army to provide range information to associated anti-aircraft artillery. There were two upgrades to the same basic system, GL/EF and GL Mk. II, both of which added the ability to accurately determine bearing and elevation.
The AN/APQ-7, or Eagle, was a radar bombsight system developed by the US Army Air Force. Early studies started in late 1941 under the direction of Luis Alvarez at the MIT Radiation Laboratory, but full-scale development did not begin until April 1943. By this time US-built, higher frequency systems promising better performance over the existing British H2S radar were entering production. Eagle's even higher resolution was considered important to Air Force planners who preferred precision bombing but were failing to deliver it, and high hopes were put on the system's abilities to directly attack small targets like docks and bridges.
Klein Heidelberg (KH) was a passive radar system deployed by the Germans during World War II. It used the signals broadcast by the British Chain Home system as its transmitter, and a series of six stations along the western coast of continental Europe as passive receivers. In modern terminology, the system was a bistatic radar. Because the system sent no signals of its own, the allies were unaware of its presence, and did not learn of the system until well after the D-Day invasion. The system is referred to as Klein Heidelberg Parasit in some references.
Searchlight Control, SLC for short but nicknamed "Elsie", was a British Army VHF-band radar system that provided aiming guidance to an attached searchlight. By combining a searchlight with a radar, the radar did not have to be particularly accurate, it only had to be good enough to get the searchlight beam on the target. Once the target was lit, normal optical instruments could be used to guide the associated anti-aircraft artillery. This allowed the radar to be much smaller, simpler and less expensive than a system with enough accuracy to directly aim the guns, like the large and complex GL Mk. II radar. In 1943 the system was officially designated Radar, AA, No. 2, although this name is rarely used.
Angle deception jamming is an electronic warfare technique used against conical scanning radar systems. It generates a false signal that fools the radar into believing the target is to one side of the boresight, causing the radar to "walk away" from the target and break its radar lock-on. It is also known as angle walk-off, angle stealing, or inverse con-scan.
The AMES Type 7, also known as the Final GCI, was a ground-based radar system introduced during World War II by the Royal Air Force (RAF). The Type 7 was the first truly modern radar used by the Allies, providing a 360 degree view of the airspace around the station out to a distance of about 90 miles (140 km). It allowed fighter interceptions to be plotted directly from the radar display, a concept known as ground controlled intercept, or GCI.
The AR-320 is a 3D early warning radar developed by the UK's Plessey in partnership with US-based ITT-Gilfillan. The system combined the receiver electronics, computer systems and displays of the earlier Plessey AR-3D with a Gilfillan-developed transmitter and planar array antenna from their S320 series. The main advantage over the AR-3D was the ability to shift frequencies to provide a level of frequency agility and thus improve its resistance to jamming.
