GB1275579A - Electronically controlled antenna system - Google Patents

Abstract

1275579 Aerials INTERNATIONAL STANDARD ELECTRIC CORP 30 Oct 1969 [1 Nov 1968] 53198/69 Heading H4A A TACAN beacon aerial array comprises a radiator surrounded by two or more concentric circular arrays of parasitic elements. Switching diodes controlled by re-circulating shift registers, which are stepped by a common clock, determine which parasitic elements are effective, so as to provide a rotating radiation pattern capable of producing two predetermined audio frequencies in a receiver. As described, a central radiator 1, Fig. 1, mounted on a counterpoise 4, is surrounded by two concentric rings 2, 3 of closely spaced parasitic monopole elements 5. The base of each parasitic element is coupled to the counterpoise via a diode which can be made conductive, when the element is effective, or non-conductive, when the element is inhibited, by switching signals applied through an R.F. choke (Fig. 2, not shown). A rotating nine-lobed cardioid type TACAN radiation pattern is produced by progressively enabling the diodes of selected parasitic elements in the rings 2, 3. This is effected by coupling a master clock 11 to two programmed re-circulating shift registers, the first of which has its separate bins coupled to the innermost ring of parasitic elements 2, and the second of which has its separated bins coupled to the outermost ring of parasitic elements 3. In another embodiment, in order to obtain an aerial which is operative over two frequency bands, four concentric rings of parasitic elements, two inner, and two outer, are provided (Fig. 3, not shown). In use, only the elements in one inner ring and in the corresponding outer ring are made effective at a time. The parasitic elements may be of dipole form (Fig. 4, not shown), and may be stacked as shown in Fig. 5 to improve vertical directivity. In this arrangement diodes 24, 25, 26 at the centres of the dipoles are separately coupled to bifilar R.F. chokes 22, 23, which provide a path for control switching signals.