Active electronically scanned array
An active electronically scanned array is a type of phased array antenna, a computer-controlled array antenna in which the beam of radio waves can be electronically steered to point in different directions without moving the antenna. In the AESA, each antenna element is connected to a small solid-state transmit/receive module under the control of a computer, which performs the functions of a transmitter and/or receiver for the antenna; this contrasts with a passive electronically scanned array, in which all the antenna elements are connected to a single transmitter and/or receiver through phase shifters under the control of the computer. AESA's main use is in radar, these are known as active phased array radar; the AESA is a more advanced, second-generation of the original PESA phased array technology. PESAs can only emit a single beam of radio waves at a single frequency at a time; the AESA can radiate multiple beams of radio waves at multiple frequencies simultaneously. AESA radars can spread their signal emissions across a wider range of frequencies, which makes them more difficult to detect over background noise, allowing ships and aircraft to radiate powerful radar signals while still remaining stealthy.
Bell Labs proposed replacing the Nike Zeus radars with a phased array system in 1960, was given the go-ahead for development in June 1961. The result was the Zeus Multi-function Array Radar, an early example of an active electronically steered array radar system. ZMAR became MAR when the Zeus program ended in favor of the Nike-X system in 1963; the MAR was made of a large number of small antennas, each one connected to a separate computer-controlled transmitter or receiver. Using a variety of beamforming and signal processing steps, a single MAR was able to perform long-distance detection, track generation, discrimination of warheads from decoys, tracking of the outbound interceptor missiles. MAR allowed the entire battle over a wide space to be controlled from a single site; each MAR, its associated battle center, would process tracks for hundreds of targets. The system would select the most appropriate battery for each one, hand off particular targets for them to attack. One battery would be associated with the MAR, while others would be distributed around it.
Remote batteries were equipped with a much simpler radar whose primary purpose was to track the outgoing Sprint missiles before they became visible to the distant MAR. These smaller Missile Site Radars were passively scanned, forming only a single beam instead of the MAR's multiple beams; the first Soviet APAR, the 5N65, was developed in 1963-1965 as a part of the S-225 ABM system. After some modifications in the system concept in 1967 it was built at Sary Shagan Test Range in 1970-1971 and nicknamed Flat Twin in the West. Four years another radar of this design was built on Kura Test Range, while the S-225 system was never commissioned; the first military ground-based AESA was the J/FPS-3 which became operational with the 45th Aircraft Control and Warning Group of the Japan Self-Defense Forces in 1995. The first series production ship-based AESA was the OPS-24, a fire-control radar introduced on the Japanese Asagiri-class destroyer DD-155 Hamagiri launched in 1988; the first airborne series production AESA was the EL/M-2075 Phalcon on a Boeing 707 of the Chilean Air Force that entered service in 1994.
The first AESA on a combat aircraft was the J/APG-1 introduced on the Mitsubishi F-2 in 1995. The first AESA on a missile is the seeker head for the AAM-4B, an air-to-air missile carried by the Mitsubishi F-2 and Mitsubishi-built McDonnell-Douglas F-15J. US based manufacturers of the AESA radars used in the F-22 and Super Hornet include Northrop Grumman and Raytheon; these companies design and manufacture the transmit/receive modules which comprise the'building blocks' of an AESA radar. The requisite electronics technology was developed in-house via Department of Defense research programs such as MMIC Program. Radar systems work by connecting an antenna to a powerful radio transmitter to emit a short pulse of signal; the transmitter is disconnected and the antenna is connected to a sensitive receiver which amplifies any echos from target objects. By measuring the time it takes for the signal to return, the radar receiver can determine the distance to the object; the receiver sends the resulting output to a display of some sort.
The transmitter elements were klystron tubes or magnetrons, which are suitable for amplifying or generating a narrow range of frequencies to high power levels. To scan a portion of the sky, the radar antenna must be physically moved to point in different directions. Starting in the 1960s new solid-state devices capable of delaying the transmitter signal in a controlled way were introduced; that led to the first practical large-scale passive electronically scanned array, or phased array radar. PESAs took a signal from a single source, split it into hundreds of paths, selectively delayed some of them, sent them to individual antennas; the radio signals from the separate antennas overlapped in space, the interference patterns between the individual signals was controlled to reinforce the signal in certain directions, mute it in all others. The delays could be controlled electronically, allowing the beam to be steered quickly without moving the antenna. A PESA can scan a volume of space much quicker than a traditional mechanical system.
Additionally, thanks to progress in electronics, PESAs added the ability to produce several active beams, allowing them to continue scanning the sky while at the same time focusing smaller beams on certain targets for tracking or guiding
Heavy machine gun
A heavy machine gun or HMG is a class of machine gun implying greater characteristics than general purpose or medium machine guns. There are two recognized classes of weapons identified as heavy machine guns; the first are weapons from World War I identified as "heavy" due to the weight and encumberment of the weapons themselves. The second are large-caliber machine guns, pioneered by John Moses Browning with the M2 machine gun, designed to provide increased range and destructive power against vehicles, buildings and light fortifications beyond the standard rifle calibers used in medium or general-purpose machine guns, or the intermediate cartridges used in light machine guns; the term was used to refer to the generation of machine guns which came into widespread use in World War I. These fired standard rifle cartridges such as the 7.92 Mauser.303 British or 7.62×54mmR, but featured heavy construction, elaborate mountings, water-cooling mechanisms that enabled long-range sustained automatic fire with excellent accuracy.
However, these advantages came at the cost of being too cumbersome to move as well as requiring a crew of several soldiers to operate them. Thus, in this sense, the "heavy" aspect of the weapon referred to the weapon's bulk and ability to sustain fire, not the cartridge caliber; this class of weapons was best exemplified by the Maxim gun, invented by the American inventor Hiram Maxim, who had traveled to England to market his design and became a British subject in 1900. The Maxim was the most ubiquitous machine gun of World War I, variants of which were fielded by three separate warring nations; the modern definition refers to a class of large-caliber machine guns, pioneered by John Moses Browning with the M2 machine gun. These weapons are designed to provide increased range and destructive power against vehicles, buildings and light fortifications beyond the standard rifle calibers used in medium or general-purpose machine gun, or the intermediate cartridges used in light machine guns. In this sense, the "heavy" aspect of the weapon refers to its superior power and range over light- and medium-caliber weapons, in addition to its weight.
This class of machine gun came into widespread use during World War II, when the M2 was used in fortifications, on vehicles and in aircraft by American forces. A similar HMG capacity was fielded by the Soviets in the form of Vasily Degtyaryov's DShK in 12.7×108mm. The ubiquitous German MG42 general-purpose machine gun, though well-suited against infantry, lacked the M2's anti-fortification and anti-vehicle capability, a fact, noted and lamented by the Germans; the continued need for a longer-range machine gun with anti-materiel capability to bridge the gap between anti-infantry weapons and anti-materiel weapons has led to the widespread adoption and modernization of the class, most nations' armed forces are equipped with some type of HMG. Machine guns with calibers smaller than 10mm are considered medium or light machine guns, while those larger than 15mm are classified as autocannons instead of heavy machine guns. In the late 19th century, Gatling guns and other externally powered types such as the Nordenfelt were made in a variety of calibers, such as 0.5-inch and 1-inch.
Due to their multiple barrels, overheating was not so much of an issue, but they were quite heavy. When Maxim developed his recoil-powered machine gun using a single barrel, his first main design weighed a modest 26 pounds and fired a.45-inch rifle-caliber bullet from a 24-inch barrel. A famous photo of Maxim showed him picking it up by its 15-pound tripod with one arm, it was similar to present-day medium machine guns, but it could not be fired for extended periods due to overheating. As a result, Maxim created a water jacket cooling system to enable it to fire for extended periods. However, this added significant weight. There were thus two main types of heavy, rapid-fire weapons: the manually powered, multiple-barrel machine guns and the single-barrel Maxim guns. By the end of the 19th century, many new designs such as the M1895 Colt–Browning and Hotchkiss were developed, powered by gas operation or recoil operation. Rather than the heavy water jacket, new designs introduced other types of barrel cooling, such as barrel replacement, metal fins, heat sinks or some combination of these.
Machine guns diverged into lighter designs. The model water-cooled Maxim guns and its derivatives the MG 08 and the Vickers, as well as the American M1917 Browning machine gun, were all substantial weapons. The.303 Vickers, for example, weighed 33 lb and was mounted on a tripod that brought the total weight to 50 lb. The heavier designs could, in some cases did, fire for days on end in fixed defensive positions to repel infantry attacks; these machine guns were mounted on tripods and were water-cooled, a well-trained crew could fire nonstop for hours, given sufficient ammunition, replacement barrels and cooling water. Positioned heavy machine guns could stop an attacking force before they reached their objectives. However, during the same period a number of lighter and more portable air-cooled designs were developed weighing less than 30 lbs. In World War I they were to be as important as the heavier designs, were used to support infantry on the attack, on aircraft, on many types of vehicles.
The lightest of the new designs were not capable of sustained automatic fire, as they did
Peacekeeping refers to activities intended to create conditions that favour lasting peace. Research finds that peacekeeping reduces civilian and battlefield deaths and reduces the risk of renewed warfare. Within the United Nations group of nation-state governments and organisations, there is a general understanding that at the international level, peacekeepers monitor and observe peace processes in post-conflict areas, may assist ex-combatants in implementing peace agreement commitments that they have undertaken; such assistance may come in many forms, including confidence-building measures, power-sharing arrangements, electoral support, strengthening the rule of law, economic and social development. Accordingly, the UN peacekeepers can include soldiers, police officers, civilian personnel; the United Nations is not the only organisation to implement peacekeeping missions. Non-UN peacekeeping forces include the NATO mission in Kosovo and the Multinational Force and Observers on the Sinai Peninsula or the ones organised by the European Union and the African Union.
The Nonviolent Peaceforce is one NGO considered to have expertise in general peacemaking by non-governmental volunteers or activists. Under international law, peacekeepers are non-combatants due to their neutral stance in the conflict between two or more belligerent parties and are to be protected from attacks at all times. There are a range of various types of operations encompassed in peacekeeping. In Page Fortna's book Does Peacekeeping Work?, for instance, she distinguishes four different types of peacekeeping operations. These types of missions and how they are conducted are influenced by the mandate in which they are authorized. Three of Fortna's four types are consent-based missions, i.e. so-called "Chapter VI" missions, with the fourth being a "Chapter VII" Mission. Chapter VI missions are consent based, therefore they require the consent of the belligerent factions involved in order to operate. Should they lose that consent, Peacekeepers would be compelled to withdraw. Chapter VII missions, by contrast, do not require consent.
If consent is lost at any point, Chapter VII missions would not be required to withdraw. Observation Missions which consist of small contingents of military or civilian observers tasked with monitoring cease-fires, troop withdrawals, or other conditions outlined in a ceasefire agreement, they are unarmed and are tasked with observing and reporting on what is taking place. Thus, they do not possess the capability or mandate to intervene should either side renege on the agreement. Examples of observation missions include UNAVEM II in Angola in 1991 and MINURSO in the Western Sahara. Interpositional Missions known as traditional peacekeeping, are larger contingents of armed troops meant to serve as a buffer between belligerent factions in the aftermath of a conflict. Thus, they serve as a buffer zone between the two sides and can monitor and report on the compliance of either side with regard to parameters established in a given ceasefire agreement. Examples include UNAVEM III in Angola in 1994, MINUGUA in Guatemala in 1996.
Multidimensional missions are carried out by military and police personnel in which they attempt to implement robust and comprehensive settlements. Not only do they act as observers, or in an interpositional role, but they participate in more multidimensional tasks—such as electoral supervision and security forces reform, institution building, economic development and more. Examples include UNTAG in Namibia, ONUSAL in El Salvador, ONUMOZ in Mozambique. Peace enforcement Missions are Chapter VII missions and unlike the previous Chapter VI missions, they do not require the consent of the belligerent parties; these are multidimensional operations comprising both military personnel. The military force is substantial in size and well-equipped by UN Peacekeeping standards, they are mandated to use force for purposes beyond just self-defence. Examples include ECOMOG and UNAMSIL in West Africa and Sierra Leone in 1999, as well as the NATO operations in Bosnia—IFOR and SFOR. During the Cold War, peacekeeping was interpositional in nature—thus being referred to as traditional peacekeeping.
UN Peacekeepers were deployed in the aftermath of interstate conflict in order to serve as a buffer between belligerent factions and ensure compliance with the terms of an established peace agreement. Missions were consent-based, more than not observers were unarmed—such was the case with UNTSO in the Middle East and UNCIP in India and Pakistan. Others were armed -- such as UNEF-I, they were successful in this role. In the post-Cold War era, the United Nations has taken on a more nuanced, multidimensional approach to Peacekeeping. In 1992, in the aftermath of the Cold War Secretary-General Boutros Boutros-Ghali put together a report detailing his ambitious concepts for the United Nations and Peacekeeping at large; the report, titled An Agenda for Peace, described a multi-faceted and interconnected set of measures he hoped would lead to effective use of the UN in its role in post-Cold War international politics. This included the use of preventative diplomacy, peace-enforcement, peace-making, peace-keeping and post-conflict reconstruction.
In The UN Record on Peacekeeping Operations, Michael Doyle and Nicolas Sambanis summarise Boutros Boutros’ report as preventative diplomacy, confidence-bu
Anti-ship missiles are guided missiles that are designed for use against ships and large boats. Most anti-ship missiles are of the sea skimming variety, many use a combination of inertial guidance and active radar homing. A good number of other anti-ship missiles use infrared homing to follow the heat, emitted by a ship; the first anti-ship missiles, which were developed and built by Nazi Germany, used radio command guidance. These saw some success in the Mediterranean Theater in 1943–44, sinking or damaging at least 31 ships with the Henschel Hs 293 and more than seven with the Fritz X, such as the Italian battleship Roma or the cruiser USS Savannah. A variant of the HS 293 had a TV transmitter on board; the bomber carrying it could fly outside the range of naval AA guns and use TV guidance to lead the missile to its target by radio control. Many anti-ship missiles can be launched from a variety of weapons systems including surface warships, bombers, fighter planes, patrol planes, shore batteries, land vehicles, conceivably by infantrymen firing shoulder-launched missiles.
The term surface-to-surface missile is used. The longer-range anti-ship missiles are called anti-ship cruise missiles. A typical abbreviation for the phrase "anti-ship missile" is ASM, but AShM can be used to avoid confusion with air-to-surface missiles, anti-submarine missiles, anti-satellite missiles. Anti-ship missiles were among the first instances of short-range guided missiles during World War II in 1943–44; the German Luftwaffe used the Hs 293, the Fritz X, others, all launched from its bombers, to deadly effect against some Allied ships in the Mediterranean Sea damaging ships such as the United States Navy light cruiser USS Savannah off Salerno, Italy. These all used radio command-guidance from the bombardiers of the warplanes; some of these hit and either sank or damaged a number of ships, including warships offshore of amphibious landings on western Italy. These radio-controlled missiles were used until the Allied navies developed missile countermeasures—principally radio jamming; the Allies developed some of their own similar radio-guided AShMs, starting with the U.
S. Navy's SWOD-9 Bat – the first autonomously-guided, radar-homing anti-ship weapon deployed worldwide, being deployed against the Japanese in April 1945 – but the Bat saw little use in combat from its own late-war deployment date. During the Cold War, the Soviet Union turned to a sea-denial strategy concentrating on submarines, naval mines and the AShM. One of the first products of the decision was the SS-N-2 Styx missile. Further products were to follow, they were soon loaded onto the Soviet Air Force's Tu-95 Bear and Tu-22 Blinder bombers, in the case of the air-launched KS-1 Komet. In 1967, the Israeli Navy's destroyer Eilat was the first ship to be sunk by a ship-launched missile – a number of Styx missiles launched by Egyptian Komar-class missile boats off the Sinai Peninsula. In the Indo-Pakistani War of 1971 the Indian Navy conducted two raids using OSA 1-class missile boats employing the Styx on the Pakistani Naval base at Karachi; these raids resulted in the destruction or crippling of two thirds of the Pakistani Navy.
Major losses included two destroyers, a fleet oiler, an ammunition ship a dozen merchant ships and numerous smaller craft. Major shore based facilities, including fuel storage tanks and naval installations were destroyed; the Osas returned to base without loss. The Battle of Latakia in 1973 was the scene of the world's first combat between missile boats. In this battle, the Israeli Navy destroyed Syrian warships without suffering any damage, using electronic countermeasures and ruses for defense. After defeating the Syrian navy the Israeli missile boats sank a number of Egyptian warships, again without suffering any damage in return, thus achieving total naval supremacy for the rest of the war. Anti-ship missiles were used in the 1982 Falklands War; the British warship HMS Sheffield, a 4,820 ton Type 42 Destroyer, was struck by a single air-launched Exocet AShM, she sank as a result of the damage that she sustained. The container ship Atlantic Conveyor was sunk by an Exocet. HMS Glamorgan was damaged when she was struck by an MM38 missile launched from an improvised trailer-based launcher taken from the Argentine Navy destroyer ARA Comodoro Seguí by Navy technicians, but she was able to take evasive action that restricted the damage.
In 1987, a US Navy guided-missile frigate, the USS Stark, was hit by an Exocet anti-ship missile fired by an Iraqi Mirage F-1 fighter plane. Stark was damaged. In October 1987, the Sungari, an American-owned tanker steaming under the Liberian flag, a Kuwaiti tanker steaming under the American flag, the Sea Isle City, were hit by Iranian HY-2 missiles. In 1988 ASMs were fired by both American and Iranian forces in Operation Praying Mantis in the Persian Gulf. During this naval battle, several Iranian warships were hit by American ASMs; the US Navy hit the Iranian Navy light frigate IS Sahand with three Harpoon missiles, four AGM-123 Skipper rocket-propelled bombs, a Walleye tv-guided bomb, several 1,000 lb "iron bombs". Despite the large number of munitions and successful hits, the 1,540 ton IS Sahand did not sink until fire reached her ammunition magazine, causing it to detonate, sinking the vessel. In the same engagement, American w
A variable-pitch propeller or controllable-pitch propeller is a type of propeller with blades that can be rotated around their long axis to change the blade pitch. Reversible propellers—those where the pitch can be set to negative values—can create reverse thrust for braking or going backwards without the need to change the direction of shaft revolution. Propellers whose blade pitch could be adjusted while the aircraft was on the ground were used by a number of early aviation pioneers, including A. V. Roe and Louis Breguet. In 1919 L. E. Baynes AFRAeS patented the first automatic variable-pitch airscrew; the French aircraft firm Levasseur displayed a variable-pitch propeller at the 1921 Paris Airshow, which, it claimed, had been tested by the French government in a ten-hour run and could change pitch at any engine RPM. Dr Henry Selby Hele-Shaw and T. E. Beacham patented a hydraulically operated variable-pitch propeller in 1924 and presented a paper on the subject before the Royal Aeronautical Society in 1928, though it was received with scepticism as to its utility.
The propeller had been developed with Gloster Aircraft Company — as the Gloster Hele-Shaw Beacham Variable Pitch Propellor — and was demonstrated on a Gloster Grebe, where it was used to maintain a near-constant RPM. The first practical controllable-pitch propeller for aircraft was introduced in 1932. French firm Ratier pioneered variable-pitch propellers of various designs from 1928 onwards, relying on a special ball bearing helicoidal ramp at the root of the blades for easy operation. Several designs were tried, including a small bladder of pressurized air in the propeller hub providing the necessary force to resist a spring that would drive the blades from fine pitch to coarse pitch. At a suitable airspeed a disk on the front of the spinner would press sufficiently on the bladder's air-release valve to relieve the pressure and allow the spring to drive the propeller to coarse pitch; these "pneumatic" propellers were fitted on the DH88 Comet aircraft, winner of the famed long distance 1934 Mac Robertson race and in the Caudron C.460 winner of the 1936 National Air Races, flown by Michel Detroyat.
Use of these pneumatic propellers required presetting the propeller to fine pitch prior to take-off. This was done by pressurizing the bladder with a bicycle pump, hence the whimsical nickname Gonfleurs d'hélices given to the aircraft ground mechanics in France up to this day; such propellers are used in propeller-driven aircraft to adapt the propeller to different thrust levels and air speeds so that the propeller blades don't stall, hence degrading the propulsion system's efficiency. For cruising, the engine can operate in its most economical range of rotational speeds. With the exception of going into reverse for braking after touch-down, the pitch is controlled automatically without the pilot's intervention. A propeller with a controller that adjusts the blade pitch so that the rotational speed always stays the same is called a constant-speed propeller. A propeller with controllable pitch can have a nearly constant efficiency over a range of airspeeds. A common type of controllable-pitch propeller is hydraulically actuated.
This design led to the award of the Collier Trophy of 1933. de Havilland subsequently bought up the rights to produce Hamilton propellers in the UK, while the British company Rotol was formed to produce its own designs. The French company of Pierre Levasseur and Smith Engineering Co. in the United States developed controllable-pitch propellers. Smith propellers were used by Wiley Post on some of his flights. Another common type was developed by Wallace R. Turnbull and refined by the Curtiss-Wright Corporation; this electrically-operated mechanism was first tested in on June 6, 1927 at Camp Borden, Ontario and patented in 1929. It was favoured by some pilots in World War II, because when the engine was no longer running the propeller could be feathered. On hydraulically-operated propellers the feathering had to happen before the loss of hydraulic pressure in the engine; as experimental aircraft and microlights have become more sophisticated, it has become more common for such light aeroplanes to fit variable-pitch propellers, both ground-adjustable propellers and in-flight-variable propellers.
Hydraulic operation is too expensive and bulky, instead light aircraft use propellers that are activated mechanically or electrically. The Silence Twister prototype kitplane was fitted with the V-Prop, an automatic self-energising and electronically self-adjusting VP propeller. A variable-pitch propeller can be efficient for the full range of rotational speeds and load conditions, since its pitch will be varied to absorb the maximum power that the engine is capable of producing; when loaded, a vessel needs more propulsion power than when empty. By varying the propeller blades to the optimal pitch, higher efficiency can be obtained, thus saving fuel. A vessel with a VPP can accelerate faster from a standstill, can decelerate much more making stopping quicker and safer. A VPP can improve vessel maneuverability by directing a stronger flow of water onto the rudder. However, a fixed-pitch propeller is both cheaper and more robust than a VPP. An FPP is more efficient than a VPP for a single specific rotational speed and load condition.
Accordingly, vessels that operate at a standard speed will have an FPP optimized for that speed. At the other extreme, a canal narrowboat will have a FPP for two reasons: speed is
Manoeuvring thruster is a transversal propulsion device built into, or mounted to, either the bow or stern, of a ship or boat to make it more maneuverable. Bow thrusters make docking easier, since they allow the captain to turn the vessel to port or starboard side, without using the main propulsion mechanism which requires some forward motion for turning. A stern thruster is of the same principle, fitted at the stern. Large ships might have multiple bow thrusters and stern thrusters. Large vessels have one or more tunnel thrusters built into the bow, below the waterline. An impeller in the tunnel can create thrust in either direction. Most tunnel thrusters are driven by electric motors; these bow thrusters known as tunnel thrusters, may allow the ship to dock without the assistance of tugboats, saving the costs of such service. Ships equipped with tunnel thrusters have a sign marked above the waterline over each thruster on both sides, as a big cross in a red circle:. Tunnel thrusters increase the vessel's resistance to forward motion through the water, but this can be mitigated through proper fairing aft of the tunnel aperture.
Ship operators should take care to prevent fouling of the tunnel and impeller, either through use of a protective grate or by cleaning. During vessel design, it is important to determine whether tunnel emergence above the water surface is commonplace in heavy seas. Tunnel emergence hurts thruster performance, may damage the thruster and the hull around it. Instead of a tunnel thruster, boats from 30 to 80 feet in length may have an externally mounted bow thruster; as its name suggests, an external bow thruster is attached to the bow, making it suitable for boats where it is impossible or undesirable to install a tunnel thruster, due to hull shape or outfitting. Externally mounted bow thrusters have one or more propellers driven by a small reversible electric motor which provides thrust in either direction; the added control provided by a bow thruster helps the captain to avoid accidents while docking. A waterjet thruster is a special type of bow thruster that utilizes a pumping device instead of a conventional propeller.
The water is discharged through specially designed nozzles which increase the velocity of the exiting jet. Waterjets have the advantage of smaller hull penetrations for an equivalent size thruster. Additionally, the higher exit velocity of the discharged water increases the relative efficiency as speeds of advance, or currents, increase, as compared to standard tunnel thrusters; some waterjet bow thrusters can be configured to provide forward and aft auxiliary propulsion, or full 360 degree thrust. Reaction control system Nautic Expo on Bow Thrusters How Bow Thruster is Used for Maneuvering a Ship? by Marine Insight, September 13, 2012, By Amitava Chakrabarty Sail Magazine, on Upgrade: Installing a Bow Thruster, By Roger Marshall, Dec. 3, 2012
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, spacecraft, guided missiles, motor vehicles, weather formations, 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. Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed. Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of 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 a common noun, losing all capitalization.
The modern uses of radar are diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, range-controlled radar for public health surveillance. High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from high noise levels. Radar is a key technology that the self-driving systems are designed to use, along with sonar and other sensors. Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "lidar". 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, 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 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 a patent for a related amendment for estimating the distance to the ship.
He got a British patent on September 23, 1904 for 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 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 to airmen and during 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 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 when aircraft flew overhead.
Across the Atlantic in 1922, after placing a transmitter and receiver on opposite sides of the Potomac River, U. S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through 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 continue the work. Eight years Lawrence A. Hyland at the Naval Research Laboratory observed similar fading effects from passing aircraft. Before the Second World War, researchers in the United Kingdom, Germany, Japan, the Netherlands, the Soviet Union, the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, New Zealand, South Africa followed prewar Great Britain's radar development, Hungary 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 Télégraphie Sans Fil headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locatin