A new method of generating a rotating radiation polar diagram

In recent years, there has been a tendency to introduce new navigational aids which utilize rotating aerial arrays of large electrical dimensions in order to obtain highly accurate navigational information; one such example is the well-known system called Tacan. In general, the rotation of large arrays introduces severe mechanical problems which fix a lower limit of about 300 Mc/s to the operating radio frequencies of these aids. For many purposes it is desirable to operate in the 100 Mc/s region, and the paper describes a method by which this object may be achieved. Briefly, it consists of rotating an aerial array of small mechanical dimensions and allowing it to be coupled electrically to a static array of very large dimensions which acts as the final radiator of electromagnetic energy. The efficiency of coupling and the form of the static array are such as to produce a final radiation which makes the rotatable array appear to have the large dimensions of the static array. In effect, the method is similar to the familiar `goniometer¿ technique. The method is described with reference to its application in a new and more accurate form of Vor system (v.h.f. omni-range) known as Vorac. The paper also describes how the new method itself helps to improve the vertical elevational performance of a conventional Vor system.