Author :
Sarage, W. ; Hadley, D.T. ; Moss, F.
Abstract :
A ?first model? of an experimental high-speed analogue computer and pattern tracer for the radiation patterns of two-dimensional arrays (the pattern is traced in less than 1/50 sec) is described and the application of such instruments to the design of arrays with specified required patterns discussed. The design of arrays with a minimum number of separate aerials, which meet given pattern specifications (within specified tolerance limits) is usually a very tedious and cumbersome trial-and-error procedure. In such a situation any suitable computing apparatus is of help by simplifying and reducing the duration of each separate trial. A high-speed computer-tracer has the additional advantage that it enables the designer not only to compute quickly a sequence of trial patterns, but to try to obtain a satisfactory approximation to the required pattern by direct visual curve fitting on the screen of the c.r.o. When a satisfactory pattern has been obtained, the corresponding array (i.e. the positions of the individual aerials and their current amplitudes and phases) is directly and completely determined by the positions of the manual controls of the analogue. The model described is limited to 2-aerial and 3-aerial arrays and the maximum distances of the aerials from a reference point are at present of the order of 1??, but these limitations are not inherent in the chosen method of analogue representation, and probably arrays consisting of more than five aerials with maximum distances of more than 3? could be successfully investigated and designed by means of a computer of the type under discussion. The paper deals with some general array design problems, with the analogue relation used as the basis of the computer and with the detail design of the computer. Special points which are emphasized and discussed in detail are as follows:? 1. The ?design apparatus? aspect of high-speed computers with instantaneous indication of the result is discussed and their operation is inter- - preted as the application of an ideally ?perfect? graphical curve selection or approximation method. 2. The two-fold non-uniqueness of solutions obtained by the analogue computer is emphasized and it is shown that it is due to two reasons:?(a) the same pattern can be obtained by arrays with completely different individual aerial currents, (b) the same ideally required pattern curve can be approximated by different physically possible pattern curves. 3. An RC variable phase-shifting circuit with dissipation compensation is described. 4. A simple single-valve pulse generator of the ?voltage-gate? type is described which serves, when driven by a saw-tooth wave voltage, as a pulse position modulator and phase modulator. It is thought that this pulse generator is of general interest, apart from its application described here.
