Radar Division

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(NB This text is an extract from the late Harry Cole's unpublished work "The History of the Marconi Radar Company" 1997.)

The successes of the early sixties gave the Radar company a growing reputation in the international market-place, both in the civil and military spheres. Now began a tremendous spurt of sales of the S600 radars in the military area. In the decade '67 to '77, 74 systems were sold world-wide.

The sales figures for this period of Radar Division's history show, on a five-year running-average basis, £4 million in 1956 rising to £30 million in 1967. In 1977 the order book was in excess of £150 million. The first half of the '70s saw a massive increase in business for the S600 military systems, finding markets in unlikely places such as the former Yugoslavia, which proved to be a very big customer over a long period of years.

Development of the S600 series was still going on in the late '60s: Product Planning had carried out a world­ wide survey of primary radar ATC requirements. It showed that the world was looking to 23cm for the future with high priority being given to anti-clutter performance plus reliability. In an attempt to improve MTI performance, some manufacturers had modified their existing antenna designs to include a second beam by the addition of another feed horn. It had less gain at the lower elevation angles. The idea behind this was that by reducing the gain at very low elevations — which would include ground clutter - and keeping higher gain at higher elevation angles - which included aircraft­ - there would be an improvement in the overall aircraft-to-ground-clutter ratio. The upper beam of course would be used in a 'receive only mode, having its own separate receiver. A simple coaxial change­-over switch would allow beam selection at a given range, thus preserving the full force of the main beam's gain at low elevations outside regions of high-level local clutter. This 'add-on' approach meant compromise in the antenna performance, for the second beam's feed put up antenna blockage and the reflector's profile had been designed only for a single beam.

In response to this, the Antenna Department at Baddow designed a double-curvature antenna with dual beams formed by two horns at a long focal length. It was designed from the outset specifically to produce the best enhancement of aircraft-to-ground-clutter ratio at low elevations and with emphasized gain at high elevation, so that any swept gain applied to reduce the main beam's gain at short ranges would not unduly eat into high cover at close ranges. This became the first antenna specially designed for the ATC role having dual beam operation. The S600's L-band transmitter/receiver and signal processor was simply modified to include a range-dependent changeover switch and the whole system formed the S654. The first of these radars was installed in 1972 as the bedrock of a Military ATC radar system for the Royal Canadian Air Force at Lahr in Germany with a companion system far away in British Colombia at Comox, just north of Vancouver. These were both established as the second of a two­-phase programme, the first phase being the installation of standard S600 L-band primary radars. The first phase, in Comox in 1970, began with the crash delivery (in nine months) of the primary radar by Hercules air-lift. The success of the S654 led to its being supplied to Saudi Arabia in the SIMCATS Project.

In the Naval sphere, the PX430 study into the design of an anti-missile system had crystallized into Sea Wolf in 1970 and major parts of the system were designed in 1971. Work on an Infantry Patrol Radar was still going on and the FPPS system was preceding apace.

Despite the busyness of people with work on hand, thoughts for the future were still bubbling up. The S600 series was based on an operational principle which, in turn, was part of a philosophy of the time; this was that the provision of Radar Air Defence facilities by a 3D radar, although possible, was too inflexible and expensive to be practicable at the time — far better to have modular 2D Surveillance radars, backed by a small height-finder and making them all easily and rapidly deployable and mobile. It was realised, of course, that the cost of 3D radars and their reliability would, in time, both be brought to acceptable levels — the company must be prepared for this and plan to use the technique of 3D for the future. As a result, the beginnings of what was to become the Marconi Radar 'flagship' — Martello — were proposed.

The first seeds were sown by research work carried out at Baddow in 1968 onwards into a new way of generating and extracting radar data. The technique entitled STAR (Storage Array Radar) was one in which a broad beam was used to 'floodlight' an area. A linear array of elements forming a receiver array with a narrow beam had phase shifters in each element so that the narrow beam could be 'steered' to particular azimuths across the floodlit area. The whole system was non-rotating and allowed long integration times — the received signals were 'stored' in the system permitting correlations to be sought. RRE gave the Company a contract in 1970 to build a demonstration system. From this came the precursor to Martello,­ the “Rampart” system.

Another contract inherited by the Company from Elliott was the Stand-by Local Early Warning and Control system (SLEWC). This started life as a joint project between Decca and Elliott under the MoD title of GL161. It was to provide a data handling equipment, giving autonomous interception control capability to Air Defence Reporting Stations. The SLEWC installations were modified to include the use of SSR/IFF data in its digital processing inputs and, in one, a simulator facility was also included which provided software for later exploitation in other marketing areas. Much profitable business was created by this, including the ability to extend our capabilities in the ATC radar market. The contract was completed in 1974.

Elliott Automation was a pioneer of digital tech­nology and its Airspace Control Division brought to Marconi Radar the data handling elements of automated air defence systems, digital processing of SSR signals and the then new technology of digital radar simulation systems. These were of tremendous use to those engaged in the training of fighter controllers and air traffic controllers. Elliotts had been responsible for developing this technology under RRE sponsorship and brought contracts with them when they joined Marconi. I got first-hand knowledge of the usefulness of the techniques of radar simulation when I inherited systems responsibility for a contract to supply the Egyptian Air Force with two simulator systems. Their value to the user lay in the realism created by the system which allowed extremely life­-like scenarios to be presented to students without the need for actual aircraft flights, thus avoiding the enormous expense of flying and the hazards of real-life interceptions going wrong. The Elliott 905 computer and its peripheral equipment generated radar signals to simulate ground and weather clutter, radar signals generated by aircraft, complete with 'target glint', realistic vertical polar diagrams with mountain 'shadowing' where appropriate and IFF signals for friendly aircraft. Aircraft tracks could be set up and steered by 'pilots' operating one of a suite of tabular displays and keyboards upon which speed, heading, aircraft size (echoing area), state of weapons etc. could be input. The 'pilots' would be in simulated radio contact with trainee controllers who would exercise their skills by viewing the radar PPI. Thus, with these same facilities, both air traffic controllers or intercept controllers could be trained. In interceptions for added realism, the aircraft's missiles would sometimes fail in a random fashion by dint of the system 'rolling a die' upon which one face said ‘Bent Weapon’.

The two SLEWC systems were completely assembled in the Pre-Commissioning Test Area at Baddow in 1971 so that the software and all facilities could be thoroughly checked before delivery. Subsequently, about fifteen similar systems were sold to Singapore, Jordan, Kenya, Oman, Australia and the Royal Air Force.

1972 saw the hand-over of the FPPS system at West Drayton and the start of the Comox phase two programme. This went very smoothly, the S654 having had its teething troubles sorted out at the other Canadian Air Base at Lahr in Germany. It was at this station that further work on 'Angels' was carried out. The S654 had the best available MTI and anti-rain clutter facilities of the day, the antenna having circular polarization built into its feed horns. Nevertheless, in spring the display screen would sometimes become absolutely covered in what appeared to be high level noise. For a radius of 120 nautical miles, the radar was swamped with this unfamiliar clutter. It would last for long periods over a stretch of days and then subside, only to re-appear a few days later. Its movement did not always correlate with winds. The same thing occurred in the autumn and the effect ascribed to various possible causes. The main contender was 'Angels' — flocks of birds as discovered by Dr. Eastwood many years previously and reported in his book 'Radar Ornithology'. Eventually the RCAF Project Officer commissioned a study to be carried out. Fortunately, we had the services of Mr. George Rider, himself a co-worker with Dr. Eastwood on his definitive angel studies. Various techniques to isolate the strange clutter signals were tried, including an analysis of the Doppler components. No proof positive came until an old X-band narrow-beam approach radar was adapted to look straight up in the air, without scanning. Film records were made of the video output from this which could be correlated with simultaneous records of the PPI display. The make­-shift X-band radar had resolution enough (100ns pulse duration) to register individual birds which were seen, upon showing the film, passing through the narrow beam in great profusion. They correlated extremely well with the clutter on the PPI. Subsequent calculation showed that these birds flocked from north to south down the Rhine Valley in streams of millions during their migratory journey to sunny climes. The noise-like character of the clutter they created was caused through their flying in uncoordinated flocks; there were enough of their number in a resolution cell of the S654 to create a signal above noise and their individual motion gave no coherent Doppler signature within any specific resolution cell; hence the noise-like nature of the clutter. A quickly-designed modification to the system's Swept Gain circuits gave a selection of values from which to choose and the clutter was cleared without great sacrifice to radar performance on aircraft.

Radar Division

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