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Martello

In Martello, a row of dipoles in the same horizontal plane is used at each vertical position and the out put of an entire row is fed to a receiver from which a coherent i.f. signal is produced.

The 60 (S713) or 40 (S723) i.f. outputs are fed to the b.f.n., figure 6. Within the b.f.n., any required phase shift is achieved simply by choosing resistors of suitable values. This is made possible by first splitting the i.f. signal into 4 fixed phases in quadrature and then using resistors to achieve intermediate phases by combining appropriate signal amplitudes. Furthermore, the system is not limited merely to a single elevation beam but can be extended to produce several separate beams simultaneously.

 

 

Before deciding finally on the i.f. beam forming system, consideration was given to the better known techniques of r.f. beam forming: these were rejected on the grounds that they are not only more cumbersome and space consuming but once installed are quite inflexible. I.f. beam forming, on the other hand, has the advantage that the relatively compact self-contained and passive b.f.n., figure 7, may, if required, be replaced by another having different component values. Thus if the operational role of the radar should change, a different elevation beam pattern may be provided very simply, without touching the antenna itself.

Looking further ahead, the b.f.n. concept lends itself to the use of active rather than passive devices so that it is not difficult to achieve a rapidly adaptive beam forming system if required at some future time.

 

Generation of the multiple beams is achieved by combining the outputs of the individual receiver channels in the b.f.n. The beam shape and pointing angle is governed by a matrix which couples selected amounts of each input to the various outputs in the appropriate phase relationship. The synthesized beam contours are weighted and the crossover points controlled for optimum performance.

The b.f.n. normally provides 8 beams for the S713 and 6 or 8 for the S723. Figure 8 shows the normal 8 beam pattern for 8713 and figure 4 (again) the receiving pattern in relation to the transmission pattern. Transmission occurs within an approximately cosec2 radiation pattern so that all targets on a particular bearing are illuminated by every radar pulse.


 

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Updated 06/11/2001

Constructed by Dick Barrett

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ęCopyright 2000 - 2002 Dick Barrett

The right of Dick Barrett to be identified as author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.