(NB This text is an extract from the late Harry Cole's unpublished work "The History of the Marconi Radar Company" 1997.)

In the late 70s it was realised that a market would soon open up for a small Airfield Surveillance Radar. This was because the Plessey AR 1 — widely used throughout the world — would become obsolete. Thus, a replacement market of at least 180 sets would come into play, plus others, since the world's number of small airfields had grown during the twenty or so years that the AR1 had been exploited. A very rough market survey was done to see if we could characterize the features required to make it a sure-fire winner. Fortunately, the basic parameters were easy to lay down by reference to International specifications and recommendations, together with the Company's own accrued knowledge from years of dealing with the ATC market and the ATC community's ways of working.

The watchwords were to be: Modernity, Simplicity, Value, Reliability.

The very latest S-band technology, consistent with simplicity, led to the choice of a modern magnetron for the power generator — but with a very significant difference; it was to be driven by an all­ solid-state modulator and the two (magnetron and modulator) were to be treated as a single entity. The solid-state components chosen allowed the modulator's output pulse to be accurately tailored to match the conditions required by the magnetron to bring it into oscillation without stimulating unwanted spurious modes and spectral lines. This permitted a very high order of system stability in the whole transmission system, the key to good MTI performance.

The dual-beam antenna was revolutionary; not only did it go round and round (!), its reflector was made from carbon fibre which gave it enormous strength and a very light weight. Its corrugated horn feed provided circular polarization with the ability to feed one of the orthogonal modes into a separate receiver as a source of weather signals otherwise cancelled by the circular polarization process.

The radar's signal processor was digital and unique in that it incorporated three parallel processes; one was a straightforward zero Doppler notch filter, the second had a novel 'steerable' notch which was able to sense the radial speed of the contents of each of the small range/azimuth cells into which the surveillance area was broken, and to steer the Doppler notch filter so that its null fell at this velocity; thus, any residual weather clutter not removed by the circular polarization was further attenuated. The third channel which was put through a threshold detection process whereby the clutter signals in each of a matrix of range/azimuth cells set, automatically, a level just above the clutter in that cell. Any aircraft signals above this were delivered to the display output. Thus, the whole signal processing had sub-clutter and super-clutter visibility against both fixed and moving clutter.

The systems architecture allowed single, dual or dual diversity working and the display system was provided by a 'Locus 16' architecture, allowing suites of displays to be provided in a very flexible manner.

Another unique feature was the use of an 'inductosyn' azimuth-telling system. The inductosyn is an 'around­ the-mast' unit giving digital incrementation of 14 bits (1.32 minutes of arc per increment). Being a digital system it is possible to set its datum extremely accurately by switch operation instead of tedious rotation of the azimuth-telling unit itself.

The development programme for this new ATC radar — the S511- was completed in 1980 and pro­duction began. The first major sale was to New­castle Airport, UK, and represented the ideal example of the market at which this new radar was aimed. It was installed in 1981. Newcastle Airport was run by the Municipality and had a fast­ growing international flight schedule.

In the following year the UK CAA ordered 13 sets of the electronics to replace those of their old AR1s working into the existing antennas. Although it took a while for the 5511 to find general favour in the market place, it steadily built a reputation and achieved international sales in India, Canada, Africa, Spain and the Middle East. One of the most prestigious contracts was a 'turnkey' project to fit Jordan's Queen Noor International Airport with primary and secondary radars, a suite of large screen operational control displays plus an ATC training facility using a Simulator. It was officially opened by His Majesty King Hussain of Jordan in December 1985.

At its tenth anniversary, the S511 and its variants had clocked up £20 million of business.

One variant was the higher power S511H with a co-axial magnetron rather than the standard one, also known as Surveyor. We have recently been sent a very interesting paper regarding the development of this, together with the personal engineering story of John Seddon just retired from Thales, 69 yrs young and wishing to share his Thesis to those interested in Marconi equipment history; a worked example of how we did it, for education purposes.

Type S511

A promotional video - 1.  2.

S511 Airfield Surveillance radar - Installations

Surveyor leaflet: 1,  2,  3,  4