AMES Type 82
The AMES Type 82, also widely known by its rainbow codename Orange Yeoman, was an S-band 3D radar built by the Marconi Company and used by the Royal Air Force, initially for tactical control and later for air traffic control.
Development started in 1949 at the British Army's Radar Research and Development Establishment to provide medium-range early warning for up to sixteen anti-aircraft artillery batteries. Early in the program, the team saw the Royal Navy's Comprehensive Display System, and adapted it as the Data Handling System. This provided a semi-automated track while scan function that allowed operators to handle larger numbers of aircraft.
The system was originally designed to support AAA guns by passing data on a selected target to point the AAA's local gun laying radar. In 1953 the RAF took over the air defence role and began to move from guns to the new Bloodhound missile. They also took over the design work and gave the system the Type 82 name. The first prototype began operation that year and a second was briefly used in 1955 before being moved to the UK east coast as an operational unit in 1957. Three production units were added in 1960.
The Type 82 was withdrawn from the tactical control role in January 1963, as the data it provided for Bloodhound was now available from other radars like the AMES Type 80s. They were then repurposed as air traffic control systems, where its ability to measure range, bearing, elevation and secondary radar information in a single unit was a major advantage over previous systems. During this period they were manned by military and civilian operators. In spite of their increasing age, three of the systems lasted into the 1980s and '90s in this role.
History
Earlier systems
During World War II, the British Army had a number of radar systems used in the anti-aircraft warfare role. These included the "Gun Laying" radars that provided short-range highly-accurate aiming information, and the "Tactical Control" radars that fed less accurate but longer-range information to the GL units. It was difficult to combine these two roles into a single radar; the accuracy of the GL role required a very thin pencil beam, which was not useful for scanning large volumes of the sky in the search role.One of the most successful of the TC radars was a Canadian design known as the Zone Position Indicator that was taken into operational use as the AA No. 4 Mark IV. This was developed using the electronics of the ASV Mk. II radar combined with a rotating radar antenna and custom display system. By the late-war period, the same developers had produced a model using a cavity magnetron known as the Microwave Zone Position Indicator. The British Army purchased 150 of these sets as the AA No. 4 Mark VI, and they were delivered shortly after the war ended.
These units, and similar designs from the UK, had the problem that they did not indicate altitude. This was not a concern during the war because the information would be handed off to nearby gun-laying radars, which could determine the altitude by scanning up and down once provided with an angle to look at. As the range of the TC radars grew and they became more distant from the multiple widely dispersed gun-laying radars they worked with, some indication of altitude would be needed to help the GLs in their initial pointing. This could be accomplished by a separate height finding radar, but a single radar that could provide reasonably accurate direction and altitude would make this process easier.
3D development
The Radar Research and Development Establishment, who handled the development of radars for the Army, began exploring the idea of a 3D radar that could measure the vertical angle of the target at the same time as its bearing and range. Their solution was to split the signal into several waveguides and feed horns that were positioned in a vertical stack. Each one had a reception pattern a few degrees wide vertically, and by careful arrangement, they could be overlapped so their half-power points were lined up. The echo of a target would be received by two of these feeds at any given time, and by comparing the relative signal strengths, the elevation angle could be determined to well under a degree.Serious work on the concept began in 1947, first with a mechanically spiral-scanned X-band system, and later, various experiments with stacked feeds. At the same time, research began on the design of a new high-power 25 cm wavelength cavity magnetron, a new large-format long-persistence plan-position indicator display tube, and a data link system to send the information to as many as sixteen remote sites. By mid-1948 the basic design was complete; it would operate in the X-band at 10 cm wavelength and use ten feedhorns, each one with a 3 degree vertical beam.
To test the concept, an experimental five-beam system was operational in 1949. This used the MZPI as the transmitter and a separate lens-type receiver array. The lens consisted of short metal cylinders open on both ends and aligned with the target, or boresight. Many such cylinders were arranged to make a large grid. Radio signals travelling through the open centres of the tubes slow down, and by cutting the tubes to different lengths, the wavefront of the signal can be focused down like a traditional optical lens. At the focal point were the five receiver feed horns. The lens was synchronized to turn at the same speed as the MZPI.
Orange Yeoman
In 1949 the Ministry of Supply took over direct control of the TRE and RRDE, and assigned the 3D work the Rainbow Code "Orange Yeoman". By the end of the year the system appeared to be progressing well, with the antenna design completed and a system to feed the ten signals through a series of slip-rings successfully tested. To produce more power in total, a system was developed to feed three magnetrons in parallel. A new foldable antenna was also being tested.Meanwhile, the RAF was beginning to consider the problem of long-range fighter direction and developed a requirement for a new system to be operational by 1957. The Royal Navy had been developing its own 3D radar in this period, the Type 984 radar, and in May 1950 there was some consideration of whether or not it should be used in the RAF as well. In June 1950, the Defence Research Policy Committee studied whether the 984 or Orange Yeoman might better fill the requirement. They asked the War Office and Admiralty to consider whether a single radar would be useful for both fighter control and gun direction; fighter control demanded long range which suggested a slower scanning rate than what would be ideal for a GL radar whose primary concern is rapid notifications in changes of location.
Through this period there was a growing interest in moving from anti-aircraft guns to surface-to-air missiles, or as they are known in the UK, surface-to-air guided weapons, or SAGW. There was increasing interest in Orange Yeoman as a system to help direct these weapons, which were expected to be available in the mid-to-late 1950s. Likewise, a new GL radar under development as Yellow River was ultimately redirected to be the radar illuminator for these missiles rather than as a replacement for the AA No. 3 Mark VII used with AAA. AAA would remain in use through a transition period, and there was a desire to accurately feed the information from Orange Yeoman to their existing Mark VII radars. This led to a requirement for Orange Yeoman to have an 80% probability of producing a track that was accurate to within in position and altitude.
As the development of the antenna system appeared to be progressing well, in 1950 it was decided to add another feed horn while decreasing the beam width to 2.5 degrees. This gave a total vertical coverage of 27.5 degrees in eleven beams. However, by this time other problems appeared. A major one was that the planned S-band magnetron, the BM 735, was only available in small numbers and would rarely work when pushed beyond 1 MW of its 2 MW rated power. Additionally, the slip-ring system for feeding radio frequency power to the antenna also continued to be a problem. This led to experiments with slip-rings that fed the intermediate frequency instead, with the magnetron transmitters and first stages of the superheterodyne receivers on the rotating platform.
In June 1951, with these problems ongoing, it was decided to move ahead with all the parts that did work in order to get a production system as soon as possible. This led to a system using a single 2 MW magnetron instead of three ganged ones, feeding them via IF slip-rings, and using separate transmit and receive antennas. Metropolitan-Vickers was contracted to build a test system, which consisted of a gantry framework with two turntables at different altitudes, the lower one with the transmitter antenna and the receiver above it. The complete system was working for the first time in 1953.
Data Handling System
From 1948, there had been ongoing experimentation with a new display system that stored radar data over subsequent "sweeps" and then extracted tracking information from that data. This would provide track while scan capability that would greatly ease the task of deciding which AA guns should be trained on which targets. There was also some experimentation with sending this data to control centers using voice quality telephone lines.Near the end of 1949, the RRDE staff were shown the ongoing work on the Comprehensive Display System being developed for the Navy by Elliott Brothers. This quickly led to a project to modify the same basic system to the needs of the AA Command. The main change was the ability to take a location measurement and then offset it by a constant value before calculating the azimuth, to account for the AA guns being located some distance from the radar. This was not needed in the original version where the guns were located on the same ship as the radar. This change led to the Data Handing System project, which had delivered the individual components by the end of 1950. A complete system was built at the RRDE with help from Metrovick and British Thomson-Houston during 1951, which was able to track up to 12 targets and had two large-format displays for the direction officers. A larger system with 36 tracks was built and connected to the prototype Orange Yeoman during 1952.
At first, the system required the operators to update the information for a given track by watching the radar display and moving a cursor dot with a joystick. Due to the desired rate of updates, this required a dedicated operator for every six tracks. This was later improved by the addition of a double-integrator which could automatically update the tracks as long as the aircraft did not change its course. This greatly reduced the number of manual updates required and allowed the same number of operators to track a much larger number of aircraft. A second group injected height measurements into the storage system at a slower pace, as changes in altitude were much less frequent, so only two or three operators were required for this task. This "Analysis Group" also handled the identification friend or foe system. Finally, an "Accurate Tracking Group" would pick targets from the store for longer-term, more accurate measurements, using that data to feed off to the GL radars at the gun sites.