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87-597: The Slingsby Hengist was a British military glider designed and built by Slingsby Sailplanes Ltd . Like other British troop carrying gliders in the Second World War , it was named after military figures whose name began with H, in this case the Jute invader Hengist . The use of assault gliders by the British was prompted by the use by Germany of the DFS 230 transport glider, which

174-466: A fractal surface, such as rocks or soil, and are used by navigation radars. A radar beam follows a linear path in vacuum but follows a somewhat curved path in atmosphere due to variation in the refractive index of air, which is called the radar horizon . Even when the beam is emitted parallel to the ground, the beam rises above the ground as the curvature of the Earth sinks below the horizon. Furthermore,

261-404: A transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna , a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the objects. Radio waves (pulsed or continuous) from the transmitter reflect off the objects and return to the receiver, giving information about

348-424: A transmitter that emits radio waves known as radar signals in predetermined directions. When these signals contact an object they are usually reflected or scattered in many directions, although some of them will be absorbed and penetrate into the target. Radar signals are reflected especially well by materials of considerable electrical conductivity —such as most metals, seawater , and wet ground. This makes

435-430: A 1,500 man parachute drop and the large transport gliders that he had seen. The Luftwaffe opened a parachute school as a result in 1937. Further field testing convinced Student that a vehicle was needed to deliver the heavy weapons for the lightly armed parachute troops. This idea was dismissed until October 1938 by which time Student had risen to major-general and was appointed Inspector of Airborne Forces. Development of

522-840: A common noun, losing all capitalization . The modern uses of radar are highly diverse, including air and terrestrial traffic control, radar astronomy , air-defense systems , anti-missile systems , marine radars to locate landmarks and other ships, aircraft anti-collision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring, radar remote sensing , altimetry and flight control systems , guided missile target locating systems, self-driving cars , and ground-penetrating radar for geological observations. Modern high tech radar systems use digital signal processing and machine learning and are capable of extracting useful information from very high noise levels. Other systems which are similar to radar make use of other parts of

609-482: A different dielectric constant or diamagnetic constant from the first, the waves will reflect or scatter from the boundary between the materials. This means that a solid object in air or in a vacuum , or a significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves from its surface. This is particularly true for electrically conductive materials such as metal and carbon fibre, making radar well-suited to

696-535: A full radar system, that he called a telemobiloscope . It operated on a 50 cm wavelength and the pulsed radar signal was created via a spark-gap. His system already used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected. In 1915, Robert Watson-Watt used radio technology to provide advance warning of thunderstorms to airmen and during

783-604: A hostile beachhead, the gliders to be towed by Consolidated PBY-5A Catalina amphibian aircraft . The Navy's Bureau of Aeronautics developed specifications for two types of amphibious glider, a single-hulled type which could carry 12 passengers and a twin-hulled type that could carry 24 passengers. Two companies, the Allied Aviation Corporation and the Bristol Aeronautical Corporation , received contracts to produce 100 gliders, and plans called for

870-553: A much more capable force. The Soviets also experimented with ways to deliver light tanks by air, including the Antonov A-40 , a gliding tank with detachable wings. By the time of the Korean War , helicopters had largely replaced gliders. Helicopters have the advantage of being able to extract soldiers, in addition to delivering them to the battlefield with more precision. Also, advances in powered transport aircraft had been made, to

957-729: A physics instructor at the Imperial Russian Navy school in Kronstadt , developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter . In 1897, while testing this equipment for communicating between two ships in the Baltic Sea , he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation. The German inventor Christian Hülsmeyer

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1044-495: A proposal for further intensive research on radio-echo signals from moving targets to take place at NRL, where Taylor and Young were based at the time. Similarly, in the UK, L. S. Alder took out a secret provisional patent for Naval radar in 1928. W.A.S. Butement and P. E. Pollard developed a breadboard test unit, operating at 50 cm (600 MHz) and using pulsed modulation which gave successful laboratory results. In January 1931,

1131-698: A pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by the American Robert M. Page , working at the Naval Research Laboratory . The following year, the United States Army successfully tested a primitive surface-to-surface radar to aim coastal battery searchlights at night. This design was followed by a pulsed system demonstrated in May 1935 by Rudolf Kühnhold and

1218-442: A rescue. For similar reasons, objects intended to avoid detection will not have inside corners or surfaces and edges perpendicular to likely detection directions, which leads to "odd" looking stealth aircraft . These precautions do not totally eliminate reflection because of diffraction , especially at longer wavelengths. Half wavelength long wires or strips of conducting material, such as chaff , are very reflective but do not direct

1305-611: A study with view to develop a glider capable of being towed by aircraft. This directive was set into motion through Classified Technical Instructions (CTI-198 on 24 February 1941, and CTI-203 on 4 March 1941), which authorized the procurement of 2-, 8-, and 15-place gliders and equipment. Eleven companies were invited to participate in the experimental glider program, but only four responded with any interest, Frankfort Sailplane Company (XCG-1, XCG-2), Waco Aircraft Company (XCG-3, XCG-4), St. Louis Aircraft Corp. (XCG-5, XCG-6), and Bowlus Sailplanes (XCG-7, XCG-8). Only Waco Aircraft Company

1392-662: A system might do, Wilkins recalled the earlier report about aircraft causing radio interference. This revelation led to the Daventry Experiment of 26 February 1935, using a powerful BBC shortwave transmitter as the source and their GPO receiver setup in a field while a bomber flew around the site. When the plane was clearly detected, Hugh Dowding , the Air Member for Supply and Research , was very impressed with their system's potential and funds were immediately provided for further operational development. Watson-Watt's team patented

1479-722: A troop-carrying glider was assigned to Hans Jacobs of the Deutsche Forschungsanstalt für Segelflug to develop the DFS 230 which could carry 9–10 fully equipped troops or 1,200 kg (2,800 pounds). The Germans were the first to use gliders in warfare, most famously during the assault of the Eben Emael fortress and the capture of the bridges over the Albert Canal at Veldwezelt, Vroenhoven and Kanne on May 10, 1940, in which 41 DFS 230 gliders carrying 10 soldiers each were launched behind Junkers Ju 52s . Ten gliders landed on

1566-514: A wide region and direct fighter aircraft towards targets. Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate, and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships. In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters. Meteorologists use radar to monitor precipitation and wind. It has become

1653-797: A writeup on the apparatus was entered in the Inventions Book maintained by the Royal Engineers. This is the first official record in Great Britain of the technology that was used in coastal defence and was incorporated into Chain Home as Chain Home (low) . Before the Second World War , researchers in the United Kingdom, France , Germany , Italy , Japan , the Netherlands , the Soviet Union , and

1740-452: Is a simplification for transmission in a vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In a real-world situation, pathloss effects are also considered. Frequency shift is caused by motion that changes the number of wavelengths between the reflector and the radar. This can degrade or enhance radar performance depending upon how it affects

1827-451: Is as follows, where F D {\displaystyle F_{D}} is Doppler frequency, F T {\displaystyle F_{T}} is transmit frequency, V R {\displaystyle V_{R}} is radial velocity, and C {\displaystyle C} is the speed of light: Passive radar is applicable to electronic countermeasures and radio astronomy as follows: Only

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1914-560: Is intended. Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the target objects themselves, such as infrared radiation (heat). This process of directing artificial radio waves towards objects is called illumination , although radio waves are invisible to the human eye as well as optical cameras. If electromagnetic waves travelling through one material meet another material, having

2001-417: Is the range. This yields: This shows that the received power declines as the fourth power of the range, which means that the received power from distant targets is relatively very small. Additional filtering and pulse integration modifies the radar equation slightly for pulse-Doppler radar performance , which can be used to increase detection range and reduce transmit power. The equation above with F = 1

2088-492: The China-Burma-India Theater . The CG-4A was constructed of a metal and wood frame covered with fabric, manned by a crew of two and with an allowable normal cargo load of 3,710 lb, allowing it to carry 13 combat-equipped troops or a jeep or small artillery piece. The CG-10 could hold 10,850 lb of cargo, such as two howitzers , at a time. The final glider mission of the war was at Luzon on 23 June 1945. By

2175-583: The Gotha Go 242 (23 trooper) and Messerschmitt Me 321 (130 trooper) to transport heavy armaments in anticipation of Operation Sea Lion and Operation Barbarossa . Gliders were also used by Germany in Greece in 1941. On April 26, 1941, the troops from six DFS 230 gliders captured the bridge over the Corinth Canal accompanied by 40 plane-loads of German paratroopers. (Fortuitously, the British were able to demolish

2262-572: The Japanese attack on Pearl Harbor on 7 December 1941 prompted the United States to set the number of glider pilots needed at 1,000 to fly 500 eight-seat gliders and 500 fifteen-seat gliders. The number of pilots required was increased to 6,000 by June 1942. After Barringer was lost at sea on a flight to Africa in January 1943, the program came under direction of Richard C. du Pont . Bigger gliders, such as

2349-623: The Nyquist frequency , since the returned frequency otherwise cannot be distinguished from shifting of a harmonic frequency above or below, thus requiring: Or when substituting with F D {\displaystyle F_{D}} : As an example, a Doppler weather radar with a pulse rate of 2 kHz and transmit frequency of 1 GHz can reliably measure weather speed up to at most 150 m/s (340 mph), thus cannot reliably determine radial velocity of aircraft moving 1,000 m/s (2,200 mph). In all electromagnetic radiation ,

2436-714: The RAF's Pathfinder . The information provided by radar includes the bearing and range (and therefore position) of the object from the radar scanner. It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets. This evolved in the civilian field into applications for aircraft, ships, and automobiles. In aviation , aircraft can be equipped with radar devices that warn of aircraft or other obstacles in or approaching their path, display weather information, and give accurate altitude readings. The first commercial device fitted to aircraft

2523-664: The Royal Air Force in the Royal Air Force Gliding & Soaring Association and for cadet training by the Air Training Corps , they are not used in combat operations. No troop-carrying gliders have been in British service since 1957. Major General Henry "Hap" Arnold , Acting Deputy Chief of Staff for Air (becoming Commanding General of the United States Army Air Forces on March 9, 1942), initiated

2610-676: The United States Army 's capabilities on 1 January 1953. However, the United States Air Force continues to use sailplanes at the United States Air Force Academy to train cadets in the fundamentals of flight. In April 1941, United States Navy officer Marc Mitscher proposed that the Navy develop amphibious gliders with flying-boat hulls with a goal of deploying an amphibious glider force capable of delivering an entire United States Marine Corps brigade of 715 men to

2697-657: The Yakovlev Yak-14 (35 trooper) in 1948, and the Ilyushin Il-32 (60 trooper) also in 1948. In 1950, a Yak-14 became the first glider to fly over the North Pole . The Soviet Union maintained three glider infantry regiments until 1965. However, Soviet Air Force transport gliders were gradually withdrawn from service with the arrival of turboprop transports like the Antonov An-12 and Antonov An-24 , which entered service in

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2784-662: The capture of the Caen canal and Orne river bridges in a coup-de-main operation at the very start of the invasion of Normandy . Other glider actions included Operation Dragoon (the invasion of southern France), Operation Market Garden (the landing at Arnhem Bridge to try and seize a bridgehead over the lower Rhine) and Operation Varsity (crossing of the Rhine). Out of the 2,596 gliders dispatched for Operation Market Garden, 2,239 were effective in delivering men and equipment to their designated landing zones. Although gliders are still used in

2871-440: The electromagnetic spectrum . One example is lidar , which uses predominantly infrared light from lasers rather than radio waves. With the emergence of driverless vehicles, radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents. As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov ,

2958-407: The reflective surfaces . A corner reflector consists of three flat surfaces meeting like the inside corner of a cube. The structure will reflect waves entering its opening directly back to the source. They are commonly used as radar reflectors to make otherwise difficult-to-detect objects easier to detect. Corner reflectors on boats, for example, make them more detectable to avoid collision or during

3045-527: The "new boy" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units. Wilkins would select a General Post Office model after noting its manual's description of a "fading" effect (the common term for interference at the time) when aircraft flew overhead. By placing a transmitter and receiver on opposite sides of the Potomac River in 1922, U.S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through

3132-413: The 1920s went on to lead the U.K. research establishment to make many advances using radio techniques, including the probing of the ionosphere and the detection of lightning at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told

3219-770: The 30-troop Waco CG-13A and the 42-troop Laister-Kauffman CG-10 A were designed later. The most widely used type was the Waco CG-4A, which was first used in the invasion of Sicily in July 1943 and participated in the D-Day assault on France on 6 June 1944, and in other important airborne operations in Europe, including Operation Market Garden in September 1944 and the crossing the Rhine in March 1945, and in

3306-650: The Hengist with a rubber bag as a landing device. A strengthened undercarriage was used on the production aircraft and was called the Mk III, but this name was not carried over to the RAF. The Hengist had a distinctive appearance with curved upper and lower surfaces and a flat sided fuselage. Two Hengist Mk Is were delivered to the Glider Pilots' Exercise Unit while others were issued to experimental units or remained in storage. Production

3393-439: The Navy took delivery during World War II of 15 U.S. Army Air Forces Waco CG-4A non-amphibious gliders for evaluation under the Navy designation LRW-1. Neither of these initiatives resulted in operational use of gliders by the U.S. Navy or Marine Corps. The Soviet Union built the world's first military gliders starting in 1932, including the 16-seat Grokhovski G63, though no glider was built in quantity until World War II. During

3480-622: The Soviet Union demonstrated the TsK Komsula, a four-place glider, designed by GF Groschev that could also be used for cargo. Larger gliders were then developed culminating in an 18-seater at the military institute in Leningrad in 1935. Luftwaffe Colonel Kurt Student visited Moscow as part of the military collaboration programme with the Soviet Union. He reported back to his superiors in Berlin details of

3567-480: The US sometimes used them as if they were, since it was easier than recovering them. Troops landing by glider were referred to as air-landing as opposed to paratroops . Landing by parachute caused the troops to be spread over a large drop-zone and separated from other airdropped equipment, such as vehicles and anti-tank guns. Gliders, on the other hand, could land troops and ancillaries in greater concentrations precisely at

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3654-714: The United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain's radar development, Hungary and Sweden generated its radar technology during the war. In France in 1934, following systematic studies on the split-anode magnetron , the research branch of the Compagnie générale de la télégraphie sans fil (CSF) headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locating radio apparatus, aspects of which were installed on

3741-533: The arrest of Oshchepkov and his subsequent gulag sentence. In total, only 607 Redut stations were produced during the war. The first Russian airborne radar, Gneiss-2 , entered into service in June 1943 on Pe-2 dive bombers. More than 230 Gneiss-2 stations were produced by the end of 1944. The French and Soviet systems, however, featured continuous-wave operation that did not provide the full performance ultimately synonymous with modern radar systems. Full radar evolved as

3828-428: The beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not immediately continue the work. Eight years later, Lawrence A. Hyland at the Naval Research Laboratory (NRL) observed similar fading effects from passing aircraft; this revelation led to a patent application as well as

3915-480: The bridge a few hours later.) Next, General Student then convinced Hitler that Crete could be captured using only airborne troops. Consequently, on May 20, 1941, 500 German transport aircraft carrying paratroopers and 74 DFS 230 gliders took off from the Greek mainland. During the capture of the island, 5,140 German airborne troops were either killed or wounded out of the 13,000 sent. Among the 350 German planes destroyed in

4002-408: The detection of aircraft and ships. Radar absorbing material , containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection . This is the radio equivalent of painting something a dark colour so that it cannot be seen by the eye at night. Radar waves scatter in a variety of ways depending on the size (wavelength) of the radio wave and the shape of

4089-471: The detection process. As an example, moving target indication can interact with Doppler to produce signal cancellation at certain radial velocities, which degrades performance. Sea-based radar systems, semi-active radar homing , active radar homing , weather radar , military aircraft, and radar astronomy rely on the Doppler effect to enhance performance. This produces information about target velocity during

4176-411: The detection process. This also allows small objects to be detected in an environment containing much larger nearby slow moving objects. Doppler shift depends upon whether the radar configuration is active or passive. Active radar transmits a signal that is reflected back to the receiver. Passive radar depends upon the object sending a signal to the receiver. The Doppler frequency shift for active radar

4263-606: The device in patent GB593017. Development of radar greatly expanded on 1 September 1936, when Watson-Watt became superintendent of a new establishment under the British Air Ministry , Bawdsey Research Station located in Bawdsey Manor , near Felixstowe, Suffolk. Work there resulted in the design and installation of aircraft detection and tracking stations called " Chain Home " along the East and South coasts of England in time for

4350-538: The electric field is perpendicular to the direction of propagation, and the electric field direction is the polarization of the wave. For a transmitted radar signal, the polarization can be controlled to yield different effects. Radars use horizontal, vertical, linear, and circular polarization to detect different types of reflections. For example, circular polarization is used to minimize the interference caused by rain. Linear polarization returns usually indicate metal surfaces. Random polarization returns usually indicate

4437-567: The end of the war, the United States had built 14,612 gliders of all types and had trained over 6,000 glider pilots. The designs of the Waco Aircraft Company were also produced by a wide variety of manufacturers including Ford Motor Company and Cessna Aircraft Company as well as furniture, piano and coffin manufacturers. Following World War II, the United States maintained only one regiment of gliders. Gliders were used in military exercises in 1949, but glider operations were deleted from

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4524-414: The end of the war. The Junkers Ju 322 Mammut ("Mammoth") was the largest such glider ever built, but it was never used operationally. Not all military gliders were planned for transport. The Blohm & Voss BV 40 was a German glider fighter designed to attack Allied bomber formations but was not used. The British glider development started in mid-1940, prompted by the assault on Eben Emael . Among

4611-473: The entire area in front of it, and then used one of Watson-Watt's own radio direction finders to determine the direction of the returned echoes. This fact meant CH transmitters had to be much more powerful and have better antennas than competing systems but allowed its rapid introduction using existing technologies. A key development was the cavity magnetron in the UK, which allowed the creation of relatively small systems with sub-meter resolution. Britain shared

4698-507: The extent that even light tanks could be dropped by parachute. And after the widespread use of radar in the military, silence in the air is no longer sufficient for concealment. The development of modern gliders was spurred by the Versailles Treaty following World War I , under the terms of which Germany was prohibited from constructing certain high powered airplanes. As a result, German aircraft designers turned their attention toward

4785-461: The firm GEMA  [ de ] in Germany and then another in June 1935 by an Air Ministry team led by Robert Watson-Watt in Great Britain. In 1935, Watson-Watt was asked to judge recent reports of a German radio-based death ray and turned the request over to Wilkins. Wilkins returned a set of calculations demonstrating the system was basically impossible. When Watson-Watt then asked what such

4872-495: The grassed roof of the fortress. Only twenty minutes after landing the force had neutralized the fortress at a cost of six dead and twenty wounded. Hitler was anxious to gain maximum publicity and so several foreign attachés were given guided tours of the fortress. Consequently, the British, American and Japanese became quickly aware of the methods that had been used. By mid-1940, both Japan and Britain had active glider programs. Development then began of even larger gliders such as

4959-427: The late 1950s. Radar Radar is a system that uses radio waves to determine the distance ( ranging ), direction ( azimuth and elevation angles ), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft , ships , spacecraft , guided missiles , motor vehicles , map weather formations , and terrain . A radar system consists of

5046-623: The objects' locations and speeds. Radar was developed secretly for military use by several countries in the period before and during World War II . A key development was the cavity magnetron in the United Kingdom , which allowed the creation of relatively small systems with sub-meter resolution. The term RADAR was coined in 1940 by the United States Navy as an acronym for "radio detection and ranging". The term radar has since entered English and other languages as an anacronym ,

5133-494: The ocean liner Normandie in 1935. During the same period, Soviet military engineer P.K. Oshchepkov , in collaboration with the Leningrad Electrotechnical Institute , produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver. The Soviets produced their first mass production radars RUS-1 and RUS-2 Redut in 1939 but further development was slowed following

5220-494: The operation, half had been Ju 52s, which seriously depleted the force needed for the invasion of the Soviet Union shortly after. As a result, Hitler vowed never to use his airborne force in such large numbers again. Some German glider operations continued later in the war, some examples being the rescue operation of Benito Mussolini at Gran Sasso and emergency re-supply operations in Russia, North Africa and Eastern Europe towards

5307-520: The outbreak of World War II in 1939. This system provided the vital advance information that helped the Royal Air Force win the Battle of Britain ; without it, significant numbers of fighter aircraft, which Great Britain did not have available, would always have needed to be in the air to respond quickly. The radar formed part of the " Dowding system " for collecting reports of enemy aircraft and coordinating

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5394-438: The practical development of unpowered aircraft, with a pilot remaining in the air in a glider for more than 20 minutes and a national glider competition emerging by 1922. The early sporting objectives of gliders were quickly overtaken in the Soviet Union and in Germany by military applications, mainly the training of pilots. By 1934, the Soviet Union had ten gliding schools and 57,000 glider pilots had gained licences. In 1932,

5481-706: The primary tool for short-term weather forecasting and watching for severe weather such as thunderstorms , tornadoes , winter storms , precipitation types, etc. Geologists use specialized ground-penetrating radars to map the composition of Earth's crust . Police forces use radar guns to monitor vehicle speeds on the roads. Automotive radars are used for adaptive cruise control and emergency breaking on vehicles by ignoring stationary roadside objects that could cause incorrect brake application and instead measuring moving objects to prevent collision with other vehicles. As part of Intelligent Transport Systems , fixed-position stopped vehicle detection (SVD) radars are mounted on

5568-507: The procurement of 12,000 more amphibious gliders if the concept proved successful. No twin-hulled glider was built, but each company constructed the prototype of a single-hulled amphibious glider, the XLRA-1 by Allied Aviation and the XLRQ-1 by Bristol Aeronautical. The two prototypes made their first flights in early 1943, but by the time they did the Navy and Marine Corps already had concluded that

5655-432: The radial component of the velocity is relevant. When the reflector is moving at right angle to the radar beam, it has no relative velocity. Objects moving parallel to the radar beam produce the maximum Doppler frequency shift. When the transmit frequency ( F T {\displaystyle F_{T}} ) is pulsed, using a pulse repeat frequency of F R {\displaystyle F_{R}} ,

5742-414: The response. Given all required funding and development support, the team produced working radar systems in 1935 and began deployment. By 1936, the first five Chain Home (CH) systems were operational and by 1940 stretched across the entire UK including Northern Ireland. Even by standards of the era, CH was crude; instead of broadcasting and receiving from an aimed antenna, CH broadcast a signal floodlighting

5829-410: The resulting frequency spectrum will contain harmonic frequencies above and below F T {\displaystyle F_{T}} with a distance of F R {\displaystyle F_{R}} . As a result, the Doppler measurement is only non-ambiguous if the Doppler frequency shift is less than half of F R {\displaystyle F_{R}} , called

5916-427: The roadside to detect stranded vehicles, obstructions and debris by inverting the automotive radar approach and ignoring moving objects. Smaller radar systems are used to detect human movement . Examples are breathing pattern detection for sleep monitoring and hand and finger gesture detection for computer interaction. Automatic door opening, light activation and intruder sensing are also common. A radar system has

6003-407: The scattered energy back toward the source. The extent to which an object reflects or scatters radio waves is called its radar cross-section . The power P r returning to the receiving antenna is given by the equation: where In the common case where the transmitter and the receiver are at the same location, R t = R r and the term R t ² R r ² can be replaced by R , where R

6090-467: The target landing area. Furthermore, the glider, once released at some distance from the actual target, was effectively silent and difficult for the enemy to identify. Larger gliders were developed to land heavy equipment like anti-tank guns , anti-aircraft guns, small vehicles, such as jeeps , and also light tanks (e.g., the Tetrarch tank ). This heavier equipment made otherwise lightly armed paratroop forces

6177-491: The target. If the wavelength is much shorter than the target's size, the wave will bounce off in a way similar to the way light is reflected by a mirror . If the wavelength is much longer than the size of the target, the target may not be visible because of poor reflection. Low-frequency radar technology is dependent on resonances for detection, but not identification, of targets. This is described by Rayleigh scattering , an effect that creates Earth's blue sky and red sunsets. When

6264-519: The technology with the U.S. during the 1940 Tizard Mission . In April 1940, Popular Science showed an example of a radar unit using the Watson-Watt patent in an article on air defence. Also, in late 1941 Popular Mechanics had an article in which a U.S. scientist speculated about the British early warning system on the English east coast and came close to what it was and how it worked. Watson-Watt

6351-547: The tow craft near the front, they were to land on any convenient open terrain close to the target, hopefully with as little damage to the cargo and crew as possible, as most landing zones (LZ) were far from ideal. The one-way nature of the missions meant that they were treated as semi-expendable leading to construction from common and inexpensive materials such as wood. Most nations seriously attempted to recover as many as possible, to re-use them, so they were not originally intended to be disposable, although resource-rich nations like

6438-879: The transmitter. The reflected radar signals captured by the receiving antenna are usually very weak. They can be strengthened by electronic amplifiers . More sophisticated methods of signal processing are also used in order to recover useful radar signals. The weak absorption of radio waves by the medium through which they pass is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light , infrared light , and ultraviolet light , are too strongly attenuated. Weather phenomena, such as fog, clouds, rain, falling snow, and sleet, that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapour, raindrops, or atmospheric gases (especially oxygen) are avoided when designing radars, except when their detection

6525-487: The two length scales are comparable, there may be resonances . Early radars used very long wavelengths that were larger than the targets and thus received a vague signal, whereas many modern systems use shorter wavelengths (a few centimetres or less) that can image objects as small as a loaf of bread. Short radio waves reflect from curves and corners in a way similar to glint from a rounded piece of glass. The most reflective targets for short wavelengths have 90° angles between

6612-547: The types developed were the 28 trooper Airspeed Horsa and the 7-ton capacity General Aircraft Hamilcar cargo glider. The Hamilcar could carry vehicles, anti-tank guns and light tanks into action. The General Aircraft Hotspur – originally planned as a compact assault glider carrying a small number of troops – was used for training the British Army pilots who formed the Glider Pilot Regiment . The Slingsby Hengist

6699-467: The use of radar altimeters possible in certain cases. The radar signals that are reflected back towards the radar receiver are the desirable ones that make radar detection work. If the object is moving either toward or away from the transmitter, there will be a slight change in the frequency of the radio waves due to the Doppler effect . Radar receivers are usually, but not always, in the same location as

6786-560: The use of gliders to deliver Marines to beachheads was impractical. No further examples of the two glider types were built, and the Navy officially terminated the amphibious glider program on 27 September 1943. Testing of the two prototypes continued until early December 1943, apparently in connection with the development of a glider bomb. The Marine Corps established a glider training unit in early 1942 at Marine Corps Recruit Depot Parris Island , South Carolina , using non-amphibious Pratt-Read LNE-1 and Schweizer LNS-1 gliders. In addition,

6873-625: The war, there were only two light gliders built in series: Antonov A-7 and Gribovski G-11 – about 1,000 altogether. A medium glider, the KC-20 , was built in a small series. They were used mostly for providing partisans in Belarus with supplies and armament in 1942–1943. On 21 September 1943, 35 gliders were used in the Dnepr crossing . Later, other types of gliders were built: the Cybin C-25 (25 trooper) in 1944,

6960-608: Was a 1938 Bell Lab unit on some United Air Lines aircraft. Aircraft can land in fog at airports equipped with radar-assisted ground-controlled approach systems in which the plane's position is observed on precision approach radar screens by operators who thereby give radio landing instructions to the pilot, maintaining the aircraft on a defined approach path to the runway. Military fighter aircraft are usually fitted with air-to-air targeting radars, to detect and target enemy aircraft. In addition, larger specialized military aircraft carry powerful airborne radars to observe air traffic over

7047-508: Was a backup design which was not required when the similar capacity American-built Waco CG-4 (given the British service name "Hadrian") became available in large numbers through lend-lease. Four hundred of the 3,600 Horsas built were supplied to the USAAF. The most famous British actions using gliders included the unsuccessful Operation Freshman , against a German heavy water plant in Norway in 1942; and

7134-467: Was able to deliver the experimental glider prototypes that satisfied the requirements of Materiel Command, the eight-seat Waco CG-3 (modified to become a production nine-seat glider) and the fifteen-seat Waco CG-4 . In October 1941, Lewin B. Barringer was made Glider Specialist, Air Staff, HQ of the Army Air Forces, answering to General Arnold, and placed in charge of the glider program. The shock of

7221-504: Was first used in May 1940 to land assault troops on the Eben Emael fort in Belgium . Their advantage compared to parachute assault was that the troops landed in one place, rather than being dispersed. The Slingsby T.18 Hengist was designed by John "Jack" Frost . It was a 15-seat glider designed to meet Specification X.25/40 (in accordance to O.R.98), issued in February 1941. The specification

7308-411: Was halted when Waco Hadrian gliders became available under Lend-Lease . As a back-up type, it saw no operational service and was phased out of service in 1946. Data from Slingsby Sailplanes, British Gliders and Sailplanes 1922–1970 General characteristics Performance Aircraft of comparable role, configuration, and era Related lists Military glider Once released from

7395-405: Was issued in case sufficiently powerful tugs were not available for the larger Airspeed Horsa . Four prototypes were ordered in late 1940, the first prototype DG570 flying in January 1942, towed by an Armstrong Whitworth Whitley . A total of 14 production Hengist Mk I were delivered to the Royal Air Force (RAF) between February 1943 and March 1944. One of Frost's unique design touches was to fit

7482-748: Was sent to the U.S. in 1941 to advise on air defense after Japan's attack on Pearl Harbor . Alfred Lee Loomis organized the secret MIT Radiation Laboratory at Massachusetts Institute of Technology , Cambridge, Massachusetts which developed microwave radar technology in the years 1941–45. Later, in 1943, Page greatly improved radar with the monopulse technique that was used for many years in most radar applications. The war precipitated research to find better resolution, more portability, and more features for radar, including small, lightweight sets to equip night fighters ( aircraft interception radar ) and maritime patrol aircraft ( air-to-surface-vessel radar ), and complementary navigation systems like Oboe used by

7569-459: Was the first to use radio waves to detect "the presence of distant metallic objects". In 1904, he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter. He obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also obtained a British patent on 23 September 1904 for

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