Martello
(Note: A larger copy of figure 15 can
be viewed by clicking on the image - Ed.)
The turning gear assembly, which includes an existing Marconi-designed digital azimuth take-off system, is mounted on a purpose-designed monocoque trailer fitted with swing-out legs to form a stable deployment gantry. As quick deployment with the minimum of manpower was a design aim, the antenna and turning gear are attached to the trailer by a pivot and raised and lowered between roading and operating positions by a hydraulic ram operated from a single control panel. Levelling of the deployed gantry is achieved by additional hydraulic rams fitted on each of the three legs.
Radar
height accuracy at all azimuth positions is ensured by continuous electronic
monitoring of the levelling. Any deviation is fed into the height com-puting
system together with dynamic deflections of the antenna which are measured by
a gyroscopic vertical reference unit mounted in the antenna spine.
Both S713 and S723 convoys comprise a complete set of vehicles (including diesel power generators) some appropriately designed to transport the detach-able antenna sections. The antenna spine and its associated vehicle are shown in transit in figure 16.
EVOLUTION OF THE MARTELLO FAMILY
When Martello was first conceived in the 70's it was anticipated that eventually transistor technology would permit a solid state transmitter, although that stage had not then been reached. Nevertheless, the concept of separate co-phased solid state transistor output stages for each row, or set of rows, of the antenna was always kept in mind.
However, for the first Martello, S713, a conventional stable linear-beam amplifier was designed for the transmitter using a Twystron tube to give up to 3 MW peak power, 10 kW mean, at a pulse length of 10 uS, with a repetition rate around 250 p.p.s. The transmitter power is distributed to the 60 rows of dipoles by a vertical waveguide squintless feed, as shown in figure 14. Each horizontal row of 32 dipoles has a duplexer and receiver 'front-end' consisting of mixer(4) and i.f. amplifier. Gain and phase stability of the receivers is ensured at all times by an automatic pilot tone system.
After conversion to the second i.f. of 13 MHz, the signals are fed to the b.f.n. for height extraction and in subsequent stages are compressed by 40: 1 to 0.25 uS to ensure adequate range resolution.
The performance of the S713, summarized in figure 17, meets many defence specifications.
Overall radar performance results from a com-bination of many conflicting requirements including height accuracy, data rate, susceptibility to jamming, ability to see targets in clutter and these are affected, amongst other things, by the dimensions of the antenna. S713, with its 35-foot vertical and 20-foot horizontal aperture, gives excellent height accuracy and has a horizontal beamwidth of 2.8 degrees, giving a large number of pulses per target and is ideal for many defence applications.
For some other defence requirements, however, height accuracy is somewhat less significant but a narrower horizontal beam is an advantage. Thus, in the design of the S723, which occurred when tran-sistor transmitter power generation had reached a viable stage, it was decided to change to a 24-foot high by 40-foot wide antenna, divided into 40 dipole rows. This gives a slightly increased overall antenna aperture of 960 sq ft, compared with 700 sq ft.
