Radar, Air to Surface Vessel , or ASV radar for short, is a classification used by the Royal Air Force (RAF) to refer to a series of aircraft-mounted radar systems used to scan the surface of the ocean to locate ships and surfaced submarines. The first examples were developed just before the opening of World War II and they have remained a major instrument on patrol aircraft since that time. It is part of the wider surface-search radar classification, which includes similar radars in ground and ship mountings.
173-575: Radar, Air to Surface Vessel, Mark II , or ASV Mk. II for short, was an airborne sea-surface search radar developed by the UK's Air Ministry immediately prior to the start of World War II . It was the first aircraft-mounted radar of any sort to be used operationally. It was widely used by aircraft of the RAF Coastal Command , Fleet Air Arm and similar groups in the United States and Canada. A version
346-544: A Westland Sea King helicopter that was able to operate from a variety of ships. Several greatly improved versions followed, part of the Searchwater 2000 series. ASV13 and ASV21 used magnetrons , which was a technology developed during World War II. "Searchwater was a completely new concept, having a high power wideband TWT transmitter and being the first generation of ASV radars to include modern signal and data processing (digital as well as analogue)". This gave Searchwater
519-455: A 20-mile wide path. Submarines were not fast enough to cross that distance before the aircraft had returned for another sweep. There was some discussion of giving it a special display to make interpretation easier, but it went into service using the original ASV display instead. In early 1940 there was a lengthy debate within the Air Ministry, and the government in general, about whether or not
692-413: A U-boat was carried out by a Swordfish on 21 December 1941. ASV had not been designed to detect submarines, but late 1939 testing by Hudsons of No. 220 Squadron RAF against HMS L27 showed that it was possible to pick up surfaced submarines at limited range and in low sea states. Experiments demonstrated that the main problem causing short range was the low gain of the antennas. Given the low speeds of
865-607: A Whitley Mk. VI damaged U-71 in the Bay of Biscay . On 26 May 1941, a Fairey Swordfish equipped with Mk. II detected the Bismarck as it attempted to return to France for repairs. This detection led to the Bismark ' s sinking the next day. By mid-1941 the ASV radar had increased daytime attacks on U-boats by 20%, and made night attacks possible for the first time. The first successful night attack on
1038-426: A better ability than ASV13 or ASV21 to detect small targets such as submarine periscopes against a background of strong sea returns. The radar screen for Searchwater could be viewed in daylight, unlike the screen of ASV21, which was viewed in a radar 'tent' on board the aircraft. From Watts and Smith: Antenna (radio) In radio engineering , an antenna ( American English ) or aerial ( British English )
1211-581: A bomber at about 1,000 yards (910 m) at most, whereas the accuracy of the CH system was perhaps 5 miles (8.0 km). He wrote a memo on the topic on 27 April 1936 and sent it to Hugh Dowding , who was at that time the Air Member for Research and Development , and copied Robert Watt at the CH research center at Bawdsey Manor in Suffolk. Watt met with his researchers at the local Crown and Castle pub, and agreed that
1384-405: A boom; the boom is only for support and not involved electrically. Only one of the elements is electrically connected to the transmitter or receiver, while the remaining elements are passive. The Yagi produces a fairly large gain (depending on the number of passive elements) and is widely used as a directional antenna with an antenna rotor to control the direction of its beam. It suffers from having
1557-446: A collection of early combat reports was compiled in order to better understand how to improve the system. By this time the Mk. I had also been installed on Blackburn Botha and Bristol Beaufort aircraft. The reports noted that the system was useful for detecting ships at night or in bad weather, but suffered from the fact that enemy shipping typically hugged the coastline where the returns from
1730-405: A current of 1 Ampere will require 63 Volts, and the antenna will radiate 63 Watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the current induced by the signal would arrive at the antenna's feedpoint out-of-phase with the signal, causing the net current to drop while the voltage remains
1903-463: A current will reflect when there are changes in the electrical properties of the material. In order to efficiently transfer the received signal into the transmission line, it is important that the transmission line has the same impedance as its connection point on the antenna, otherwise some of the signal will be reflected backwards into the body of the antenna; likewise part of the transmitter's signal power will be reflected back to transmitter, if there
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#17329061955282076-495: A fashion are known to be harmonically operated . Resonant antennas usually use a linear conductor (or element ), or pair of such elements, each of which is about a quarter of the wavelength in length (an odd multiple of quarter wavelengths will also be resonant). Antennas that are required to be small compared to the wavelength sacrifice efficiency and cannot be very directional. Since wavelengths are so small at higher frequencies ( UHF , microwaves ) trading off performance to obtain
2249-400: A feed-point impedance that matches that of a transmission line; a matching network between antenna terminals and the transmission line will improve power transfer to the antenna. A non-adjustable matching network will most likely place further limits the usable bandwidth of the antenna system. It may be desirable to use tubular elements, instead of thin wires, to make an antenna; these will allow
2422-436: A flux of 1 pW / m (10 Watts per square meter) and an antenna has an effective area of 12 m , then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts RMS at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source. Due to reciprocity (discussed above)
2595-403: A greater bandwidth. Or, several thin wires can be grouped in a cage to simulate a thicker element. This widens the bandwidth of the resonance. Amateur radio antennas that operate at several frequency bands which are widely separated from each other may connect elements resonant at those different frequencies in parallel. Most of the transmitter's power will flow into the resonant element while
2768-450: A long Beverage antenna can have significant directivity. For non directional portable use, a short vertical antenna or small loop antenna works well, with the main design challenge being that of impedance matching . With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance ; small loop antennas are tuned with parallel capacitors for this purpose. An antenna lead-in
2941-603: A number of parallel dipole antennas with a certain spacing. Depending on the relative phase introduced by the network, the same combination of dipole antennas can operate as a "broadside array" (directional normal to a line connecting the elements) or as an "end-fire array" (directional along the line connecting the elements). Antenna arrays may employ any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop or slot antennas. These elements are often identical. Log-periodic and frequency-independent antennas employ self-similarity in order to be operational over
3114-541: A problem with noise from the ignition system interfering with the receiver, but this was soon resolved by fitters at the Royal Aircraft Establishment (RAE). On its first real test on 17 August, Anson K6260 with Touch and Keith Wood aboard immediately detected shipping in the English Channel at a range of 2 to 3 miles (3.2–4.8 km). This was particularly impressive given the very low power of
3287-427: A proper resonant antenna at the trap frequency. At substantially higher or lower frequencies the trap allows the full length of the broken element to be employed, but with a resonant frequency shifted by the net reactance added by the trap. The bandwidth characteristics of a resonant antenna element can be characterized according to its Q where the resistance involved is the radiation resistance , which represents
3460-516: A pure resistance. Sometimes the resulting (lower) electrical resonant frequency of such a system (antenna plus matching network) is described using the concept of electrical length , so an antenna used at a lower frequency than its resonant frequency is called an electrically short antenna For example, at 30 MHz (10 m wavelength) a true resonant 1 / 4 wave monopole would be almost 2.5 meters long, and using an antenna only 1.5 meters tall would require
3633-552: A range of 60 miles (97 km). Production was immediately taken up by Philco in the US and Research Enterprises Limited in Canada, with over 17,000 produced for use in the US alone. It was Mk. II equipped Fairey Swordfish that located the German battleship Bismarck in heavy overcast skies, torpedoing her and leading to her destruction the next day. Mk. II was only partially effective against
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#17329061955283806-469: A rapid re-evaluation of this stance, especially as the Soviets were known to be introducing new submarines surpassing even the late-war German designs. Adding to the problem was the loss of the large numbers of Liberator aircraft with the ending of lend-lease. These had been used as very long-range patrol aircraft during the war, and their return to the US left Coastal Command with no suitable airframes to cover
3979-501: A rather limited bandwidth, restricting its use to certain applications. Rather than using one driven antenna element along with passive radiators, one can build an array antenna in which multiple elements are all driven by the transmitter through a system of power splitters and transmission lines in relative phases so as to concentrate the RF power in a single direction. What's more, a phased array can be made "steerable", that is, by changing
4152-488: A receiver tuned to the Metox intermediate frequency that allowed them to detect the submarines at as much as 90 miles (140 km). This led to an urgent 13 August 1943 message from German Naval High Command ordering that submarines turn off their Metox. This incredible deception not only further delayed the German discovery of the true nature of the problem but also allowed Mark II to once again become effective. The reason for
4325-473: A request to fit ASV to the Armstrong Whitworth Whitley bomber, which was no longer competitive and was being passed off to other uses. Brown took the chance to develop a new antenna, a type of Sterba array , that stretched along both sides of the flat rear fuselage, firing to the side instead of forward. This "broadside array" allowed the aircraft to search wide areas of the ocean on both sides of
4498-603: A selected range to the pilot, which proved very useful for timing bomb drops. Trials were carried out in August 1944 and experimental fits were made to the Beaufighter, Mosquito and Fleet Air Arm Avengers . With the ending of World War II in 1945, the British believed another war was at least a decade off, and put little effort into new radar systems. The opening of the Cold War led to
4671-552: A shorter range that was unsuitable for closing the Gap. Coastal Command was able to have the radar switched to the ASG, which they operated under the name ASV Mark V. The TRE was sure the Germans would soon detect Mark III and render it ineffective as well, so they responded with a new ASV Mark VI that was essentially a more-powerful Mark III. The key trick to Mark VI was the "Vixen" device that allowed
4844-443: A signal into the transmission line only when the source signal's frequency is close to that of the design frequency of the antenna, or one of the resonant multiples. This makes resonant antenna designs inherently narrow-band: Only useful for a small range of frequencies centered around the resonance(s). It is possible to use simple impedance matching techniques to allow the use of monopole or dipole antennas substantially shorter than
5017-440: A smaller physical size is usually not required. The quarter-wave elements imitate a series-resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and voltage node (minimum) at the feed. In electrical terms, this means that at that position, the element has minimum impedance magnitude , generating the maximum current for minimum voltage. This
5190-498: A standard resistive impedance needed for its optimum operation. The feed point location(s) is selected, and antenna elements electrically similar to tuner components may be incorporated in the antenna structure itself, to improve the match . It is a fundamental property of antennas that most of the electrical characteristics of an antenna, such as those described in the next section (e.g. gain , radiation pattern , impedance , bandwidth , resonant frequency and polarization ), are
5363-683: A submarine schnorkel at 15 nautical miles (28 km) "in very favourable conditions but at much shorter range in the sea states normally experienced in the North Atlantic." ASV21 was generally similar to the earlier designs. ASV21 was also selected for the Mark II models of the Canadair CP-107 Argus , replacing the American AN/APS-20 of the Argus Mark I's. The Argus was widely described as
ASV Mark II radar - Misplaced Pages Continue
5536-459: A surfaced submarine, and 8 nautical miles (15 km) for a submarine conning tower. "In rougher conditions, the range would be much less." By 1958, ASV13 was considered "old and rather unreliable". EMI developed a replacement, ASV Mark 21 (ASV21) , which was cleared for service use in 1958, and came into operational use in the Shackleton Mk 2 and 3 beginning in 1959. ASV21 could detect
5709-477: A total 360 degree phase change, returning it to the original signal. The current in the element thus adds to the current being created from the source at that instant. This process creates a standing wave in the conductor, with the maximum current at the feed. The ordinary half-wave dipole is probably the most widely used antenna design. This consists of two 1 / 4 wavelength elements arranged end-to-end, and lying along essentially
5882-473: A wide range of bandwidths . The most familiar example is the log-periodic dipole array which can be seen as a number (typically 10 to 20) of connected dipole elements with progressive lengths in an endfire array making it rather directional; it finds use especially as a rooftop antenna for television reception. On the other hand, a Yagi–Uda antenna (or simply "Yagi"), with a somewhat similar appearance, has only one dipole element with an electrical connection;
6055-461: Is a monopole antenna, not balanced with respect to ground. The ground (or any large conductive surface) plays the role of the second conductor of a monopole. Since monopole antennas rely on a conductive surface, they may be mounted with a ground plane to approximate the effect of being mounted on the Earth's surface. More complex antennas increase the directivity of the antenna. Additional elements in
6228-434: Is a change in electrical impedance where the feedline joins the antenna. This leads to the concept of impedance matching , the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching is accomplished by a circuit called an antenna tuner or impedance matching network between the transmitter and antenna. The impedance match between
6401-417: Is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This
6574-490: Is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient. A necessary condition for the aforementioned reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral ) means that
6747-410: Is adjusted according to the receiver tuning. On the other hand, log-periodic antennas are not resonant at any single frequency but can (in principle) be built to attain similar characteristics (including feedpoint impedance) over any frequency range. These are therefore commonly used (in the form of directional log-periodic dipole arrays ) as television antennas. Gain is a parameter which measures
6920-421: Is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receiving). It is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver . In transmission , a radio transmitter supplies an electric current to the antenna's terminals, and
7093-400: Is called an isotropic radiator ; however, these cannot exist in practice nor would they be particularly desired. For most terrestrial communications, rather, there is an advantage in reducing radiation toward the sky or ground in favor of horizontal direction(s). A dipole antenna oriented horizontally sends no energy in the direction of the conductor – this is called the antenna null – but
ASV Mark II radar - Misplaced Pages Continue
7266-407: Is connected to a transmission line . The conductor, or element , is aligned with the electrical field of the desired signal, normally meaning it is perpendicular to the line from the antenna to the source (or receiver in the case of a broadcast antenna). The radio signal's electrical component induces a voltage in the conductor. This causes an electrical current to begin flowing in the direction of
7439-438: Is equal to 1. Therefore, the effective area A eff in terms of the gain G in a given direction is given by: For an antenna with an efficiency of less than 100%, both the effective area and gain are reduced by that same amount. Therefore, the above relationship between gain and effective area still holds. These are thus two different ways of expressing the same quantity. A eff is especially convenient when computing
7612-465: Is its radiation pattern . The frequency range or bandwidth over which an antenna functions well can be very wide (as in a log-periodic antenna) or narrow (as in a small loop antenna); outside this range the antenna impedance becomes a poor match to the transmission line and transmitter (or receiver). Use of the antenna well away from its design frequency affects its radiation pattern , reducing its directive gain. Generally an antenna will not have
7785-434: Is redirected toward the desired direction, increasing the antenna's gain by a factor of at least 2. Likewise, a corner reflector can insure that all of the antenna's power is concentrated in only one quadrant of space (or less) with a consequent increase in gain. Practically speaking, the reflector need not be a solid metal sheet, but can consist of a curtain of rods aligned with the antenna's polarization; this greatly reduces
7958-418: Is the transmission line , or feed line , which connects the antenna to a transmitter or receiver. The " antenna feed " may refer to all components connecting the antenna to the transmitter or receiver, such as an impedance matching network in addition to the transmission line. In a so-called "aperture antenna", such as a horn or parabolic dish, the "feed" may also refer to a basic radiating antenna embedded in
8131-410: Is the ideal situation, because it produces the maximum output for the minimum input, producing the highest possible efficiency. Contrary to an ideal (lossless) series-resonant circuit, a finite resistance remains (corresponding to the relatively small voltage at the feed-point) due to the antenna's resistance to radiating , as well as any conventional electrical losses from producing heat. Recall that
8304-416: Is the radio equivalent of an optical lens . An antenna coupling network is a passive network (generally a combination of inductive and capacitive circuit elements) used for impedance matching in between the antenna and the transmitter or receiver. This may be used to minimize losses on the feed line, by reducing transmission line's standing wave ratio , and to present the transmitter or receiver with
8477-440: Is unidirectional, designed for maximum response in the direction of the other station, whereas many other antennas are intended to accommodate stations in various directions but are not truly omnidirectional. Since antennas obey reciprocity the same radiation pattern applies to transmission as well as reception of radio waves. A hypothetical antenna that radiates equally in all directions (vertical as well as all horizontal angles)
8650-449: Is usable in most other directions. A number of such dipole elements can be combined into an antenna array such as the Yagi–Uda in order to favor a single horizontal direction, thus termed a beam antenna. The dipole antenna, which is the basis for most antenna designs, is a balanced component, with equal but opposite voltages and currents applied at its two terminals. The vertical antenna
8823-448: The 1 / 4 or 1 / 2 wave , respectively, at which they are resonant. As these antennas are made shorter (for a given frequency) their impedance becomes dominated by a series capacitive (negative) reactance; by adding an appropriate size " loading coil " – a series inductance with equal and opposite (positive) reactance – the antenna's capacitive reactance may be cancelled leaving only
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#17329061955288996-478: The ASV Mark 13 (ASV13) . The main improvements were the addition of stabilization so the image did not change when the aircraft manoeuvred, and the use of a pressurised radome that kept out humidity and made it suitable for use in tropical areas. ASV13 was a centimetric radar with a detection range in a calm sea ( Sea State 1 ) of about 40 nautical miles (74 km) for a destroyer, 20 nautical miles (37 km) for
9169-620: The BBC 's experimental 45 MHz television service and had built receivers that they still might have on-hand. Bowen visited the company in April or May, and found that they had "scores and scores" of the receivers in a production-ready form. When they tested them, they were found to be far superior to the EMI models. Much of the improvement in the Pye receiver was due to the use of a new type of tube developed by Philips ,
9342-707: The Consolidated B-24 Liberator , which had the range to operate over the Mid-Atlantic Gap , and an example of this aircraft with the DMS-1000 was sent to the UK for testing in early 1942. Another 30 arrived with a mix of DMS-1000, SCR-517 and ASG. However, when Bomber Command decided the Boeing B-17 Flying Fortress was unsuitable for bombing operations, the Air Ministry ordered Coastal Command to take over their existing orders in spite of them having
9515-504: The EF50 "Miniwatt", which had been designed specifically for efficient VHF use. The tubes were labeled Mullard, Philip's UK subsidiary. When they investigated, Mullard told the Air Ministry that the tubes were actually built at Philips' factory in Eindhoven , and that attempts to start production in the UK had failed due to problems manufacturing the bases. The bases used a new design that was key to
9688-508: The Harwich docks miles south of Bawdsey. Shipping also appeared, but the team was unable to test this very well as the Heyford was forbidden to fly over water. With this accidental discovery of ship detection, the team was given two Avro Anson maritime patrol aircraft , K6260 and K8758 , along with five pilots stationed at nearby RAF Martlesham Heath to test this role. Early tests demonstrated
9861-465: The half-wave dipole being a common solution. CH worked at wavelengths on the order of 10 metres, which called for antennas about 5 metres (16 ft) long, far too large to be practically carried on an aircraft. Through 1936 the team's primary concern was the development of radio systems operating at much shorter wavelengths, eventually settling on a set working at 6.7 m, based on an experimental television receiver built at EMI . In early 1937
10034-405: The lens antenna . The antenna's power gain (or simply "gain") also takes into account the antenna's efficiency, and is often the primary figure of merit. Antennas are characterized by a number of performance measures which a user would be concerned with in selecting or designing an antenna for a particular application. A plot of the directional characteristics in the space surrounding the antenna
10207-403: The resonance principle. This relies on the behaviour of moving electrons, which reflect off surfaces where the dielectric constant changes, in a fashion similar to the way light reflects when optical properties change. In these designs, the reflective surface is created by the end of a conductor, normally a thin metal wire or rod, which in the simplest case has a feed point at one end where it
10380-623: The ASV lineage. The first such example is the Seaspray , a small unit designed to be mounted on the Westland Lynx . This was originally developed in concert with the Sea Skua missile to allow the Lynx to attack fast attack craft at long range from their carrier ships. It has since been sold around the world and used in a variety of roles. The latest versions, Seaspray 7000, are completely rebuilt and share only
10553-475: The Airborne Group received a number of Western Electric Type 316A doorknob vacuum tubes. These were suitable for building transmitter units of about 20 W continual power for wavelengths of 1 to 10 m. Percy Hibberd built a new push–pull amplifier using two of these tubes working at 1.25 m wavelength; below 1.25 m the sensitivity dropped off sharply. Gerald Touch converted the EMI receiver to
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#173290619552810726-574: The GIUK gap. A solution was found by adapting surplus Bomber Command Avro Lancaster bombers with Mark VII to become the Lancaster GR.3. The use of Roman numerals had become passé by this point, and these units were referred to as ASV Mark 7A , remaining in service until 1954. A more suitable custom-built patrol aircraft was a priority and led to the Avro Shackleton . The Shackleton Mk 1 and 2 mounted
10899-497: The NRC had started working on an ASV radar using an adapted radio altimeter built by Westinghouse Electric in the US. This set worked on the relatively short wavelength of 67 cm, about half that of the British 1.5 m set. A prototype was working by November and was making some progress. The Tizard mission was in Ottawa for only two days before leaving for Washington. During that time
11072-410: The NRC radio teams pored over the ASV unit, trying to learn everything they could of its design before it left for the US. This led to a debate on whether to continue development of their own system, whose shorter wavelength would make it more suitable for aircraft use, or to simply build the British unit using Canadian and US tubes. Air-to-surface-vessel radar The first ASV was developed after
11245-563: The Netherlands was proceeding and the docks were under constant threat of air attack. By the end of July 1939, the team finally had everything in place and an order for twenty-four units was sent out. Metrovick would build the transmitters, Pye was already ramping up production of what became known as the Pye strip receiver, and Pye had also begun experimental production of a cathode ray tube (CRT) that proved suitable for radar use. In early August,
11418-699: The RAF's H2S radars. Naxos provided very short detection range, about 8 kilometres (5.0 mi), too short to be really useful. Better detectors arrived very late in the war, but by that time the U-boat force had largely been destroyed. The magnetron was revealed to the United States in 1940 during the Tizard Mission , and local development began at the MIT Radiation Laboratory in a matter of weeks. US development
11591-583: The Type 286, and 200 such units would eventually be fitted to destroyers and torpedo boats. Meanwhile, Bernard Lovell had arrived at Perth, and through contacts in the Air Ministry, managed to convince them that the site was unsuitable for their work. A new location at RAF St. Athan in Wales was selected and the team moved into a hangar on the airfield in November 1939. Conditions turned out to be little better than Perth, and
11764-424: The U-boat fleet had already been decimated. A series of other ASVs were developed for different aircraft as the war progressed. In the post-war era, several new ASV radars were developed, notably ASV Mark 7A , ASV Mark 13 and ASV Mark 21 . By the late 1960s the original terminology was no longer being used, and the last major entries in the series were known simply as Searchwater and Seaspray . Development of
11937-465: The U-boat making it impossible to dive, and flares to mark the location for follow-up attacks by other aircraft carrying depth charges . Further developments of this system led to the Mark XIII, used on de Havilland Mosquitos , Bristol Beaufighters and Bristol Brigands . The Beaufighter, which became one of Coastal Command's primary strike fighters , had the problem that the fitting of ASV required
12110-528: The United States should be told of the many technological developments taking place in the UK. The UK was suffering from a lack of manpower and production capacity, problems the US could easily solve. They also hoped to gain access to the Norden bombsight , which was several years ahead of their version, the Automatic Bomb Sight . However, the radar concepts were believed to be among some of the most advanced in
12283-467: The X-band versions of ASV a requirement, as they had the resolution needed to detect the schnorkel . On 22 November 1944, it was decided to deploy new 3 cm-band ASV's, with both the UK and US developing versions. However, these demonstrated poor performance against the schnorkel , and experiments with these new systems were still underway when the war ended. In the immediate post-war era, development of
12456-455: The accidental detection of wharves and cranes while testing an air-to-air radar in 1937. For a variety of reasons, ASV was easier to develop than the air-to-air variety of the same systems, and the first operational use of the Mark I followed in early 1940. A cleaned-up and repackaged version, ASV Mark II , replaced it at the end of the year, but the system was not widespread until late in 1941. ASV
12629-467: The addition of a loading coil. Then it may be said that the coil has lengthened the antenna to achieve an electrical length of 2.5 meters. However, the resulting resistive impedance achieved will be quite a bit lower than that of a true 1 / 4 wave (resonant) monopole, often requiring further impedance matching (a transformer) to the desired transmission line. For ever shorter antennas (requiring greater "electrical lengthening")
12802-444: The aircraft at the same time, a great improvement over the forward-only design. The broadside array offered about 2.5 times the gain of the original system. This allowed it to detect moderate-sized ships at 40 miles (64 km) and surfaced submarines at 10 to 15 miles (16–24 km), an enormous advance over the Mk. I style antennas. The aircraft could scan the approaches to a convoy by flying 10 miles to one side of it, sweeping
12975-435: The aircraft, although this could grow to as much as 4.5 miles (7.2 km) in high sea states. This would turn out to be an important limitation in practice, but one that was ultimately solved in a roundabout fashion. Finally, the shape of the targets as seen from the radar were ideal for detection. The side of the ship, rising vertically from the surface of the water, created a partial corner reflector . Radio signals hitting
13148-530: The aircraft, so that drag was not a significant issue compared to the AI role, the team was able to use Yagi antennas with much higher gain. Typical installations had the transmitter on the front of the nose, and two receivers under the wings, pointed outward at their half-power point , typically 22.5 degrees. Named Long-Range ASV, or LRASV for short, the new antennas became available for fitting in 1940. Shortly after moving to St. Athan in 1939, Hanbury Brown received
13321-402: The antenna consisting of a thin conductor. Antennas for use over much broader frequency ranges are achieved using further techniques. Adjustment of a matching network can, in principle, allow for any antenna to be matched at any frequency. Thus the small loop antenna built into most AM broadcast (medium wave) receivers has a very narrow bandwidth, but is tuned using a parallel capacitance which
13494-412: The antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception , an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified . Antennas are essential components of all radio equipment. An antenna is an array of conductors ( elements ), electrically connected to
13667-400: The antenna structure, which need not be directly connected to the receiver or transmitter, increase its directionality. Antenna "gain" describes the concentration of radiated power into a particular solid angle of space. "Gain" is perhaps an unfortunately chosen term, by comparison with amplifier "gain" which implies a net increase in power. In contrast, for antenna "gain", the power increased in
13840-474: The antenna to the power radiated by a half-wave dipole antenna I dipole {\displaystyle I_{\text{dipole}}} ; these units are called decibels-dipole (dBd) Since the gain of a half-wave dipole is 2.15 dBi and the logarithm of a product is additive, the gain in dBi is just 2.15 decibels greater than the gain in dBd High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at
14013-402: The base, tuned to operate on the ASV frequencies. The IFF system broadcast a short pulse of radio signal whenever it heard the pulse from one of the ASV radars, and its signal was so powerful that the crews could pick it up at 50 to 60 miles (80–97 km) from base, making the return flight to RAF Leuchars much less eventful. The crews took to naming the beacon "Mother". In February 1940
14186-757: The best anti-submarine aircraft of its era. ASV21D also equipped the Hawker Siddeley Nimrod MR 1 when it came into service in 1970, and was replaced by the Searchwater radar in the Nimrod MR 2 starting in 1980. ASV 21 remained in service on the Argus until the last example retired in 1981. The war-era radar classifications became less relevant in the 1970s as radar units increasingly became multi-purpose as opposed to being single-role. Newer designs, even dedicated naval surveillance designs, were not assigned numbers in
14359-402: The best solution was to introduce a small radar that could be mounted in a night fighter . If the airborne radar had a range of about 5 miles, CH could be tasked with getting the fighter into the general area, and then the fighter's own radar could take over and guide them until the enemy could be seen visually. "Taffy" Bowen asked to take on the project, and formed a small team to consider
14532-427: The broadside direction. If higher gain is needed one cannot simply make the antenna larger. Due to the constraint on the effective area of a receiving antenna detailed below , one sees that for an already-efficient antenna design, the only way to increase gain (effective area) is by reducing the antenna's gain in another direction. If a half-wave dipole is not connected to an external circuit but rather shorted out at
14705-549: The concept, Robert Watson-Watt provided the team with two Avro Ansons that were able to fly out over the North Sea from nearby RAF Martlesham Heath . The testing was crude; a small dipole antenna was hand held outside one of the escape hatches and rotated looking for when the signal disappeared, indicating the antenna was aligned with the target ship. This was not easy as the signal naturally fluctuated. The first successes were in August 1937. After several successful flights over
14878-549: The contract negotiations required considerable time to finalize, and throughout the production run it battled for precedence with the AI units and Chain Home Low which also made use of the Pye strip. The first Mk. II units began to arrive in the summer of 1940, and by October 1940, 140 transmitters, 45 receivers and 80 displays had been delivered. By the end of March 1941 that had increased to 2,000 transmitters and 1,000 receivers. Mk. II scored its first success on 30 November 1940 when
15051-453: The crews on how to best use the systems. Test flights began in late 1939, and they were used operationally in the first months of 1940. It would be some time before the related AI Mark IV sets became operational in July 1940, making ASV the world's first operational airborne radar system. At first the crews found the system relatively useless for attacks, as they could not reliably detect submarines,
15224-470: The degree of directivity of the antenna's radiation pattern . A high-gain antenna will radiate most of its power in a particular direction, while a low-gain antenna will radiate over a wide angle. The antenna gain , or power gain of an antenna is defined as the ratio of the intensity (power per unit surface area) I {\displaystyle I} radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by
15397-557: The design operating frequency, f o , and antennas are normally designed to be this size. However, feeding that element with 3 f o (whose wavelength is 1 / 3 that of f o ) will also lead to a standing wave pattern. Thus, an antenna element is also resonant when its length is 3 / 4 of a wavelength. This is true for all odd multiples of 1 / 4 wavelength. This allows some flexibility of design in terms of antenna lengths and feed points. Antennas used in such
15570-463: The desired direction is at the expense of power reduced in undesired directions. Unlike amplifiers, antennas are electrically " passive " devices which conserve total power, and there is no increase in total power above that delivered from the power source (the transmitter), only improved distribution of that fixed total. A phased array consists of two or more simple antennas which are connected together through an electrical network. This often involves
15743-405: The electromagnetic field. Radio waves are electromagnetic waves which carry signals through the air (or through space) at the speed of light with almost no transmission loss . Antennas can be classified as omnidirectional , radiating energy approximately equally in all horizontal directions, or directional , where radio waves are concentrated in some direction(s). A so-called beam antenna
15916-427: The emission of energy from the resonant antenna to free space. The Q of a narrow band antenna can be as high as 15. On the other hand, the reactance at the same off-resonant frequency of one using thick elements is much less, consequently resulting in a Q as low as 5. These two antennas may perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as
16089-407: The end of 1942, Mark II had been rendered ineffective. The introduction of the cavity magnetron in early 1940 led to efforts to develop microwave-frequency versions of the various radars then in use, including a new ASV under the name ASVS for "Sentimetric". A prototype was available from Metrovick in the summer of 1942, but they predicted it would not be widely available until summer 1943. It
16262-542: The entire area around the aircraft and displayed angles as the X-axis and range on the Y-axis. This appears to be the first example of what is today known as a B-scope . ASV proved easy to develop for a variety of reasons. One was that the host aircraft tended to be very large, so equipment size and weight were not as critical as it was in the much smaller night fighters. It was also easier to move around in these aircraft while fitting
16435-418: The entire system of reflecting elements (normally at the focus of the parabolic dish or at the throat of a horn) which could be considered the one active element in that antenna system. A microwave antenna may also be fed directly from a waveguide in place of a (conductive) transmission line . An antenna counterpoise , or ground plane , is a structure of conductive material which improves or substitutes for
16608-415: The equipment. Another reason was that these aircraft tended to fly at slower speeds, which meant that larger antennas could be used for better reception without seriously affecting aircraft performance. The early units used standard quarter-wave dipoles mounted on the nose area, but these were later extended to three-quarter wave in production units. But the major reason that ASV was easier to develop than AI
16781-526: The feedline and antenna is measured by a parameter called the standing wave ratio (SWR) on the feedline. Consider a half-wave dipole designed to work with signals with wavelength 1 m, meaning the antenna would be approximately 50 cm from tip to tip. If the element has a length-to-diameter ratio of 1000, it will have an inherent impedance of about 63 ohms resistive. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal reflection. Feeding that antenna with
16954-430: The feedpoint, then it becomes a resonant half-wave element which efficiently produces a standing wave in response to an impinging radio wave. Because there is no load to absorb that power, it retransmits all of that power, possibly with a phase shift which is critically dependent on the element's exact length. Thus such a conductor can be arranged in order to transmit a second copy of a transmitter's signal in order to affect
17127-486: The first ASV Mark III 's began arriving in March 1943, and had largely replaced the Mark II in front-line units by the end of the summer. The Germans had no way to detect these signals, and their submarines were repeatedly attacked with no warning. The losses were so great they took to leaving port in the day, but the RAF responded with strike aircraft patrols and losses shot up once again. In August, shipping losses to submarines
17300-438: The focal point of parabolic reflectors for both transmitting and receiving. Starting in 1895, Guglielmo Marconi began development of antennas practical for long-distance, wireless telegraphy, for which he received the 1909 Nobel Prize in physics . The words antenna and aerial are used interchangeably. Occasionally the equivalent term "aerial" is used to specifically mean an elevated horizontal wire antenna. The origin of
17473-446: The gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with no loss , that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ /4π , the wavelength squared divided by 4π . Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency
17646-439: The geometrical divergence of the transmitted wave. For a given incoming flux, the power acquired by a receiving antenna is proportional to its effective area . This parameter compares the amount of power captured by a receiving antenna in comparison to the flux of an incoming wave (measured in terms of the signal's power density in watts per square metre). A half-wave dipole has an effective area of about 0.13 λ seen from
17819-474: The ground. It may be connected to or insulated from the natural ground. In a monopole antenna, this aids in the function of the natural ground, particularly where variations (or limitations) of the characteristics of the natural ground interfere with its proper function. Such a structure is normally connected to the return connection of an unbalanced transmission line such as the shield of a coaxial cable . An electromagnetic wave refractor in some aperture antennas
17992-413: The increase in signal power due to an amplifying device placed at the front-end of the system, such as a low-noise amplifier . The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which the antenna delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has
18165-405: The intensity I iso {\displaystyle I_{\text{iso}}} radiated at the same distance by a hypothetical isotropic antenna which radiates equal power in all directions. This dimensionless ratio is usually expressed logarithmically in decibels , these units are called decibels-isotropic (dBi) A second unit used to measure gain is the ratio of the power radiated by
18338-555: The land often swamped the ship's returns. It was also useful for guiding an attack when the cloud cover was below 1,500 feet (460 m), as they could press an attack without ever being seen. Based on the experiences of the Mk. I units in the field, in January 1940 Gerald Touch began designing a new set while working at the RAE. Hanbury Brown joined him in February 1940. The new ASV Mk. II design
18511-417: The loading coil, relative to the decreased radiation resistance, entail a reduced electrical efficiency , which can be of great concern for a transmitting antenna, but bandwidth is the major factor that sets the size of antennas at 1 MHz and lower frequencies. The radiant flux as a function of the distance from the transmitting antenna varies according to the inverse-square law , since that describes
18684-435: The log-periodic principle it obtains the unique property of maintaining its performance characteristics (gain and impedance) over a very large bandwidth. When a radio wave hits a large conducting sheet it is reflected (with the phase of the electric field reversed) just as a mirror reflects light. Placing such a reflector behind an otherwise non-directional antenna will insure that the power that would have gone in its direction
18857-584: The long delay in discovering Mark III is somewhat surprising given that a magnetron from H2S fell into German hands almost immediately after it was first used in February 1943. Sources disagree on the reason; the magnetron was either unknown to the German Navy, or they did not believe it could be used against U-boats. It was not until late 1943 that a naval version of the Naxos radar detector arrived, having originally been developed to allow German night fighters to track
19030-443: The majority of the signal forward and away from the aircraft. The only time the signal could be seen is when the aircraft approached the water very closely when some of it would strike the water just in front of the aircraft and scattering off waves would cause a ground return. Even then the signal was relatively small compared to the huge ground return seen in the AI case, and only caused problems within about 0.5 miles (0.80 km) of
19203-553: The material has the same response to an electric current or magnetic field in one direction, as it has to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as isolators and circulators , made of nonreciprocal materials such as ferrite . These can be used to give the antenna a different behavior on receiving than it has on transmitting, which can be useful in applications like radar . The majority of antenna designs are based on
19376-564: The much smaller U-boats , especially as the signal faded as the aircraft approached the target and they would lose contact at night. To close the gap, the Leigh light was introduced, allowing the U-boat to be picked up visually after it passed off the radar display. With the introduction of the Leigh light, nighttime U-boat interceptions became common, and turned the German ports in the Bay of Biscay into deathtraps. A microwave -frequency ASV radar, ASVS,
19549-656: The name with the original models. Another example is the Searchwater , which was designed to replace the Mk. 21 in a new version of the Nimrod, the MR2. These began arriving in 1979. In 1978, the Royal Navy retired its fleet carriers, losing the Fairey Gannet AEW.3 airborne early warning aircraft. A new version of Searchwater, the LAST, was created to provide this coverage when mounted under
19722-467: The new VT90 tubes (later known as CV62) in the transmitter, while the AI Mk. II would use the older DET12 and TY120s. This meant the ASV would be somewhat more advanced than AI. Another chance encounter after the meeting led Bowen to try a new material, polythene , from Imperial Chemical Industries (ICI) which produced excellent coaxial cable and neatly solved the electrical problems they had been having. It
19895-694: The new cavity magnetron that made radars much smaller and more powerful. They were also aware of and allowed to speak about other technologies, including the jet engine and the initial concepts of the nuclear bomb detailed by the MAUD Committee . For various reasons, the mission team first travelled to Canada where they met with members of the National Research Council Canada (NRC) in Ottawa . Here they were surprised to learn that in September 1939
20068-494: The only German ships in the area. Testing had shown the maximum detection range on a surfaced submarine was about 5.5 miles (8.9 km), so in a high sea state with the minimum range of 4.5 miles, this left little room for detection. But they did find the sets useful for stationkeeping over the convoys, as well as navigating by looking at the returns from sea cliffs. But the device became extremely useful after Squadron Leader Sidney Lugg installed an IFF Mark II transponder at
20241-413: The operator to progressively mute the output as they approached the U-boat, hopefully fooling the radio operator into believing they were flying away. Mark VI never fully replaced Mark III in service, as truly effective detectors did not become available until the U-boat fleet had largely been destroyed. The failure of Naxos and later devices led to morale problems in the U-boat force. Another solution to
20414-471: The original ASV systems started in 1937 after the team testing an experimental air-to-air radar noticed odd returns while flying near the shore of the North Sea . They eventually realized these were the docks and cranes at the Harwich docks miles south of them. Shipping also appeared, but the team was unable to test this very well as their Handley Page Heyford was forbidden to fly over water. To further test
20587-653: The other parasitic elements interact with the electromagnetic field in order to realize a highly directional antenna but with a narrow bandwidth. Even greater directionality can be obtained using aperture antennas such as the parabolic reflector or horn antenna . Since high directivity in an antenna depends on it being large compared to the wavelength, highly directional antennas (thus with high antenna gain ) become more practical at higher frequencies ( UHF and above). At low frequencies (such as AM broadcast ), arrays of vertical towers are used to achieve directionality and they will occupy large areas of land. For reception,
20760-409: The other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant. An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones . Antenna gain should not be confused with amplifier gain , a separate parameter measuring
20933-464: The other side connected to ground or an equivalent ground plane (or counterpoise ). Monopoles, which are one-half the size of a dipole, are common for long-wavelength radio signals where a dipole would be impractically large. Another common design is the folded dipole which consists of two (or more) half-wave dipoles placed side by side and connected at their ends but only one of which is driven. The standing wave forms with this desired pattern at
21106-401: The others present a high impedance. Another solution uses traps , parallel resonant circuits which are strategically placed in breaks created in long antenna elements. When used at the trap's particular resonant frequency the trap presents a very high impedance (parallel resonance) effectively truncating the element at the location of the trap; if positioned correctly, the truncated element makes
21279-421: The party. On the afternoon of 3 September 1937 K6260 successfully detected the battleship HMS Rodney , the aircraft carrier HMS Courageous and the light cruiser HMS Southampton , receiving very strong returns. The next day they took off at dawn and, in almost complete overcast, detected Courageous and Southampton at a distance of 5 to 6 miles (8.0–9.7 km). As they approached
21452-461: The phases applied to each element the radiation pattern can be shifted without physically moving the antenna elements. Another common array antenna is the log-periodic dipole array which has an appearance similar to the Yagi (with a number of parallel elements along a boom) but is totally dissimilar in operation as all elements are connected electrically to the adjacent element with a phase reversal; using
21625-488: The power that would be received by an antenna of a specified gain, as illustrated by the above example. The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles in the far field. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna , which radiates equally in all directions, would look like
21798-455: The problem in August 1936. They gave the concept the name RDF2, as Chain Home was at that time known as RDF1. This would later be known as " Airborne Interception radar ", or AI for short. The major problem faced by the Airborne Group was the problem of wavelength . For a variety of reasons, an antenna with reasonable gain has to be on the same order of length as the wavelength of the signal, with
21971-469: The problem of Mark II with the introduction of the Metox radar detector . This amplified the radar's pulses and played them into the radio operator's headphones. It provided this warning long before the echos from the submarine became visible on the aircraft's display. With experience, the operators could tell whether the aircraft was approaching or just flying by, allowing the U-boat to dive and escape detection. By
22144-571: The problem of being detected was to change frequencies. From 1943, both the UK and US began developing magnetrons that worked on even shorter wavelengths, first in the X-band at 3 cm wavelength, and later in the K-band at 1.25 cm. The UK-developed 3 cm version for the Liberator became ASV Mark VII , while the US version based on ASG was known as AN/APS-15 and given the UK designation ASV Mark X. It
22317-444: The radiation pattern (and feedpoint impedance) of the element electrically connected to the transmitter. Antenna elements used in this way are known as passive radiators . A Yagi–Uda array uses passive elements to greatly increase gain in one direction (at the expense of other directions). A number of parallel approximately half-wave elements (of very specific lengths) are situated parallel to each other, at specific positions, along
22490-421: The radiation resistance plummets (approximately according to the square of the antenna length), so that the mismatch due to a net reactance away from the electrical resonance worsens. Or one could as well say that the equivalent resonant circuit of the antenna system has a higher Q factor and thus a reduced bandwidth, which can even become inadequate for the transmitted signal's spectrum. Resistive losses due to
22663-480: The radio waves into a beam or other desired radiation pattern . Strong directivity and good efficiency when transmitting are hard to achieve with antennas with dimensions that are much smaller than a half wavelength . The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the 1867 electromagnetic theory of James Clerk Maxwell . Hertz placed dipole antennas at
22836-635: The rate of two or three a week, and the crews were able to quickly fit the sets due to the easy working environment in the large fuselage. At this time, the team was large enough that they were able to send a small group to Pembroke Dock , where No. 10 Squadron RAAF was operating the Short Sunderland . The group was able to quickly fit ASV Mk. I to these aircraft, followed by the Consolidated Catalina that had also just started arriving. Meanwhile, Robert Hanbury Brown and Keith Wood began training
23009-399: The receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally ( omnidirectional antennas ), or preferentially in a particular direction ( directional , or high-gain, or "beam" antennas). An antenna may include components not connected to the transmitter, parabolic reflectors , horns , or parasitic elements , which serve to direct
23182-432: The receivers. A Metrovick employee had been told to begin building the receivers and asked for an example, but the team had only one airworthy receiver and had to give them an old hand-assembled bench model with the instructions that it wasn't to be used for a production design. Sure enough, Metrovick returned a design based on this model, which proved useless. The team also contacted Cossor and provided complete details of
23355-413: The reflection from a target. An aircraft flying at the typical German bomber altitude of 15,000 feet (4.6 km) could only see aircraft within 15,000 feet, anything beyond that was hidden in the ground return. This was a much shorter range than the 5 miles needed to close the gap with Chain Home. In comparison, when the same signal hit the water it tended to reflect rather than scatter, sending
23528-441: The reflector's weight and wind load . Specular reflection of radio waves is also employed in a parabolic reflector antenna, in which a curved reflecting surface effects focussing of an incoming wave toward a so-called feed antenna ; this results in an antenna system with an effective area comparable to the size of the reflector itself. Other concepts from geometrical optics are also employed in antenna technology, such as with
23701-485: The removal of some other devices to make room. Previously they had carried a long-distance radio for remaining in contact with their base, as well as a Gee system for navigation. Neither could be safely removed, and the desire for a much smaller ASV for this role developed. This was fulfilled with the Mark XVI, built in the US as LHTR and supplied under lend-lease . This was a very simple system originally intended to indicate
23874-529: The required design, but when they returned their first attempt six months later it was completely unusable. When they asked for improvements, Cossor never responded, too busy with other work. While waiting for the Metrovick and Cossor receivers to arrive, there was a chance encounter between Bowen and his former professor at King's College, Nobel prize winner Edward Appleton . In early 1939, Appleton mentioned to Bowen that Pye Electronics had also been interested in
24047-458: The same axis (or collinear ), each feeding one side of a two-conductor transmission wire. The physical arrangement of the two elements places them 180 degrees out of phase, which means that at any given instant one of the elements is driving current into the transmission line while the other is pulling it out. The monopole antenna is essentially one half of the half-wave dipole, a single 1 / 4 wavelength element with
24220-412: The same frequency by using it as the intermediate frequency portion of a superheterodyne circuit. The new sets were fitted to a Handley Page Heyford in March 1937. On its first flight the set demonstrated very limited range against aircraft. However, while flying the aircraft about, the operators saw odd returns appearing on the display. They finally realized these were from the wharves and cranes at
24393-425: The same whether the antenna is transmitting or receiving . For example, the "receiving pattern" (sensitivity to incoming signals as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator, even though the current and voltage distributions on the antenna itself are different for receiving and sending. This
24566-432: The same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency. The result is that the resonant antenna will efficiently feed
24739-613: The ships the Anson eventually became visible through the clouds, and the team could see the Courageous launching aircraft in a futile effort to intercept them. The weather was so bad that the operators had to use the radar as a navigation system to find their way home, using the reflection off seaside cliffs. The promise of the system was not lost on observers; Albert Percival Rowe of the Tizard Committee commented that "This, had they known,
24912-469: The signal's instantaneous field. When the resulting current reaches the end of the conductor, it reflects, which is equivalent to a 180 degree change in phase. If the conductor is 1 / 4 of a wavelength long, current from the feed point will undergo 90 degree phase change by the time it reaches the end of the conductor, reflect through 180 degrees, and then another 90 degrees as it travels back. That means it has undergone
25085-541: The submarine targets disappeared from the display just as the aircraft was readying for the attack. At night, this allowed the submarines to escape attack by maneuvering when an aircraft could be heard. This was solved by the Leigh Light , a searchlight that lit up the submarines during the last seconds of the approach. By early 1942, Mark II and the Leigh Light were finally available on large numbers of aircraft. Their effect
25258-410: The summer, Watt asked the team if they could be ready for a demonstration in September. On 4 September, the system was used to detect Royal Navy ships on manoeuvres in almost complete overcast. The weather was so bad they had to use the radar pattern from local sea-side cliffs to navigate home. Albert Percival Rowe of the Tizard Committee later commented that "This, had they known, was the writing on
25431-685: The system continued as an air-sea rescue system, as it could detect life rafts even if they did not carry a transponder . In order to upgrade the Fairey Swordfish , which had previously used the early Mark II radars, the Mark X was further adapted as the Mark XI. This used a new narrow radome that fit between the Swordfish's landing gear . The radome's location made the carriage of a torpedo impossible, so these aircraft were fit with eight RP-3 rockets with armor-piercing warheads to damage or puncture
25604-584: The target directly were returned to the receiver, but so was any signal reflecting forward off the water close to the ship, as this signal would also strike the ship and reflect back to the receiver. Whereas aircraft were difficult to detect beyond about 4 miles (6.4 km), ships could be easily detected at distances on the order of 10 miles (16 km). Any vertical surface worked in this way, including seaside cliffs, which could be picked up at very long range and proved to be extremely useful for navigation. AI and ASV developed in parallel for some time. In May 1938
25777-475: The team received the Western Electric 4304 tubes which replaced the 316As doorknobs in the transmitter and improved transmit power to 2,000 W. In testing this proved to increase detection range on ships to 12 to 15 miles (19–24 km), although in the AI role the range was little improved. While the transmitter problem was considered solved with the new tubes, the team had significant problems with
25950-452: The team was forced to work in freezing temperatures as the hangar doors had to be left open. Nevertheless, by the end of December they had managed to fit 17 AI radars in Blenheims, and 3 ASVs in the newly arriving Coastal Command Lockheed Hudsons . January improved this to 18 AI and 12 ASV, numbers that continued to increase through the year. By the early part of 1940, Hudsons were arriving at
26123-501: The team was informed that the Air Ministry had ordered 30 AI units and expected Bowen to have them installed in Bristol Blenheim aircraft within 30 days. When the units started arriving, they found the Metrovick transmitter was also the bench model, and when they protested, Metrovick noted that Watt had personally visited the factory and told them to put it into production because it was known to work. To further confuse matters, when
26296-514: The transmitter, about 100 W per pulse. By this time, Watt had moved to Air Ministry headquarters in London. He heard of the successful test and called the team to ask if they would be available for a demonstration in early September. Plans were underway to run military exercises in the Channel, including a combined fleet of Royal Navy ships and RAF Coastal Command aircraft, and Watt wanted to crash
26469-490: The wall for the German Submarine Service." Production quality sets were available in 1939 and entered operational service in early 1940, becoming the first radar system to be mounted on an aircraft in a combat setting. A somewhat improved version, Mark II, followed in 1941, which saw tens of thousands of units produced in the UK, Canada, US and Australia. These designs had a relatively long minimum range, meaning
26642-611: The war began on 1 September, the majority of the AMES team was hurriedly sent to a prearranged location at the University of Dundee in Scotland, only to find that nothing had been prepared. The rector had only vague memories of a conversation on the topic with Watt, and by now the students had returned for the fall term and there was little available room. Bowen's AI team was sent to a small airfield outside of Perth (some distance from Dundee) that
26815-508: The way the tubes operated. This led to a hurried effort to start production at the Mullard factories. The destroyer HMS Windsor was sent to the Netherlands to pick up the Philips board of directors, while two cargo ships were sent to pick up 25,000 EF50s, and 25,000 more bases which Mullard could build additional tubes while a new production line was set up. The ships left as the German attack on
26988-560: The word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi . In the summer of 1895, Marconi began testing his wireless system outdoors on his father's estate near Bologna and soon began to experiment with long wire "aerials" suspended from a pole. In Italian a tent pole is known as l'antenna centrale , and the pole with the wire was simply called l'antenna . Until then wireless radiating transmitting and receiving elements were known simply as "terminals". Because of his prominence, Marconi's use of
27161-548: The word antenna spread among wireless researchers and enthusiasts, and later to the general public. Antenna may refer broadly to an entire assembly including support structure, enclosure (if any), etc., in addition to the actual RF current-carrying components. A receiving antenna may include not only the passive metal receiving elements, but also an integrated preamplifier or mixer , especially at and above microwave frequencies. Antennas are required by any radio receiver or transmitter to couple its electrical connection to
27334-434: The world, and giving them to the US would mean surrendering some of the UK's best ideas to exploitation by what was then still a non-aligned party. Ultimately, Winston Churchill personally overrode any remaining objections, and tasked Henry Tizard with making the arrangements. After considering the many technologies being developed, Tizard's team ultimately chose four to take with them; AI Mk. IV, ASV Mk. II, IFF Mark II, and
27507-593: Was also developed for small ships, the Royal Navy 's Type 286 . The system was developed between late 1937 and early 1939, following the accidental detection of ships in the English Channel by an experimental air-to-air radar . The original ASV Mk. I entered service in early 1940 and was quickly replaced by the greatly improved Mk. II. A single Mk. II was shipped to the US during the Tizard Mission in December 1940, where it demonstrated its ability to detect large ships at
27680-405: Was at this point that the Metox started to become effective. Robert Hanbury Brown suggested a new ASV could be quickly introduced by making minor changes to the new H2S radar , mostly to the antenna. This started a furious debate between RAF Bomber Command , who wanted every H2S for their bombers, and RAF Coastal Command , who wanted them for submarine hunting. After several changes in policy,
27853-404: Was dramatic; German U-boats had previously been almost completely safe at night, and could operate out of the Bay of Biscay in spite of it being close to British shores. By the spring of 1942, Biscay was increasingly dangerous, with aircraft appearing out of nowhere in the middle of the night, dropping bombs and depth charges, and then disappearing again in moments. The Germans ultimately solved
28026-400: Was essentially a rationalized and cleaned up Mk. I, differing little in terms of the electronics, but considerably in terms of layout, wiring and construction. Among the changes was the separation of the receiver electronics from the display so either could be fixed by swapping them out separately, and using a selection of standard electrical connectors on all of the cables. As a result, Mk. II
28199-424: Was expected the latter would be available in December 1943. The similar AN/APS-3 was mounted to Catalinas and named ASV Mark VIII. In October 1944, the Germans introduced two innovations that were extremely worrying. One was the introduction of new classes of U-boats with much higher performance, and the other was the use of the schnorkel , allowing even older types to spend most of their time submerged. This made
28372-427: Was far more reliable than Mk. I; it did not offer increased performance, but maintained that performance in spite of rough service and was much easier to fix in the field. The only other major change was to move the operational frequency from 214 MHz to 176 MHz because it was found the Mk. Is were interfering with naval radio beacons . An order for 4,000 units was placed with EKCO and Pye. For reasons unknown,
28545-671: Was not subject to the infighting in the RAF, but suffered its own series of setbacks and confusion. The early DMS-1000 proved to be an excellent unit, but for reasons unknown, the US War Department decided to put the inferior Western Electric SCR-517 into production instead. Meanwhile, Philco had been developing a system for blimps , the ASG, which was much better than the SCR-517. The RAF decided that UK-built aircraft would be fitted with their Mk. III, while any US aircraft in British service would use US sets. Initially, they planned on using
28718-430: Was rushed to service, replacing the Mk. II beginning in 1943. Mk. II remained in use throughout the war in other theatres. Early during the development of the first British radar system, Chain Home (CH), Henry Tizard became concerned that the CH system would be so effective that the German air force ( Luftwaffe ) would be forced to turn to night bombing . Tizard was aware that a fighter pilot might be expected to see
28891-523: Was soon in use throughout the industry. The first ASV using production parts was hand-fitted to a Walrus and sent to Gosport for testing. This version ran at a nominal 1.5 m wavelength, at 214 MHz. Flying at only 20 feet (6.1 m) over the water, the radar easily detected ships all around the Solent. Louis Mountbatten was watching this performance and immediately ordered one fitted to his destroyer, HMS Kelly . The Navy soon picked up development as
29064-421: Was the behaviour of the very high frequency (VHF) radio waves when interacting with water. In the case of AI, when the radar's signal hit the ground it tended to scatter in all directions, sending some part of the signal back towards the aircraft. Although only a small portion of the original signal was returned, the ground was essentially infinite in size so this ground return was still much more powerful than
29237-416: Was the lowest since November 1941, and more U-boats were sunk than cargo ships. The Germans spent much of the rest of the year using radar detectors at longer wavelengths in a fruitless attempt to find the new ASV. Further confusion was added by a captured Coastal Command pilot, who related that ASV was no longer used for search, but only in the last minutes of the approach. Instead, their aircraft were using
29410-413: Was the writing on the wall for the German Submarine Service." For the next year, Bowen's team found themselves working much more on the ASV than AI. Much of this involved the development of new antenna systems, more advanced than the system on the Anson where a dipole was held outside the escape hatch and rotated by hand to hunt for signals. Among the experiments was a motorized rotating dipole that scanned
29583-421: Was under development since 1941, but the required cavity magnetrons were in limited supply and priority was given to H2S . The capture of a Mk. II-equipped Vickers Wellington by the Germans led to the introduction of the Metox radar detector tuned to its frequencies. This was soon followed by British pilots reporting submarines diving as the aircraft began to approach. A new design based on H2S, ASV Mk. III ,
29756-436: Was useful for detecting U-boats at night, but the target had to be seen to be attacked, a problem that was addressed with the Leigh light with rapidly increasing success. As German U-boat losses shot up in 1942, they concluded the RAF was using radar to detect them and responded with the Metox radar detector . The RAF responded by deploying the microwave -frequency ASV Mark III , which the Germans were unable to detect until
29929-460: Was utterly unsuitable for fitting. Nevertheless, radar sets and aircraft started to arrive, along with new demands from the Fleet Air Arm to equip some of their aircraft with ASV in Swordfish and Walrus aircraft. At a meeting in London on 30 November 1939, the relative priorities for Chain Home, Chain Home Low, AI and ASV were discussed. Bowen finalized plans to build the ASV radios at EKCO using
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