Martello
The following article from "The GEC Journal of Research", Vol. 3 No.2 1985 pages 104-113 describes the GEC S713 (R.A.F. Type 90) and S723 (R.A.F. Type 91) Martello air defence radars and has been reproduced with the kind permission of the Editor. The author, Colin Latham, has been closely associated with radar since the Chain Home (CH) days and is the author of several excellent books and papers on radar subjects.
MARTELLO - A MODERN THREE-DIMENSIONAL SURVEILLANCE RADAR
C. LATHAM
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A modern long range surveillance radar must give three-dimensional cover with good resistance to jamming, should be transportable, and capable of use autonomously or as part of a reporting system. This paper discusses these needs and the design philosophy of the Martello radar, which was conceived to meet them fully and economically. The design is discussed in some detail to show how it has evolved, and to illustrate its potential for further growth. |
INTRODUCTION
In 1985, when Martello is entering service with NATO, half a century has elapsed since the practicability of radio-location was established. From that famous Daventry experiment, the UK wartime radar chain evolved directly, and in post-war years an international radar industry has been built up.
Ever
since the lead given by CH and CHL in the war, air defence systems have continued
to rely for their essential primary sensors on long range surveillance radars,
the role for which Martello has been developed in the fourth quarter of the
century.
Frequently such long range surveillance radars are required, like CH, to provide range, bearing and height of targets and are designated '3D' (three-dimensional) but for some purposes range and bearing data only - '2D' - is acceptable. Alternatively, nodding centrimetric height finders, figure 1, have been added in some cases to 2D radars so that separately derived heights, albeit at a data rate limited by mechanical constraints, can supplement the basic range and bearing information.
GEC companies have been involved closely in the design and supply of all these classes of radars since the war, for air defence at home and abroad, and Martello represents the current state of 3D technology.
Two versions of Martello, 5713 (figure 2) and S723 (figure 3) exist currently and are described here. Whilst they differ in antenna dimensions and form of transmitter and have slightly different performance, they share many common features and employ the same principles for height finding.
BRIEF GENERAL DESCRIPTION
The two types of Martello radar are both transportable, long range air defence 3D sensors operating in L Band (23 cm). They feature frequency agility, pulse compression and comprehensive signal processing and both employ planar phased arrays to achieve minimum side-lobes for maximum resistance to jamming. The equipment is designed for military use and combines into complementary sets of vehicles, including main and standby diesel generators.
The 3D principle shown in figure 4 is applicable to any frequency but L Band was considered to be the best choice for the first generation of Martello radars: it offers a sensible compromise between the conflicting requirements of overall performance and transportability. Nevertheless some of the earlier experimental work on the planar array was carried out at S Band (10 cm) and the basis of a design was laid down for future application if required.
In addition to providing output data in agreed digital formats for feeding into defence reporting networks, Martello also incorporates its own radar displays. These permit the radar to be used auton-omously if required, but their main function is to provide a radar management centre from which decisions can be made on selection of the operational parameters of the radar, especially when in a hostile environment. Control is effected over, for example, radiated frequency, form of agility, blind arcs and other operational modes.
Both radars employ planar arrays of co-phased dipoles; these number 1920 in the S713 and 2560 in the S723. To avoid the ultimate complexity of providing that number of transmitters, duplexers and receivers, the dipoles are grouped together in rows, with a transmitter input feed, duplexer and receiver for each row.
