GB672034A - Aerial systems - Google Patents

Abstract

672,034. Aerials. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 18, 1951 [Jan. 21, 1950], No. 1656/50. Class 40 (vii). An aerial system comprises a conductive surface on which is mounted a conductive fin electrically united with the surface, the dimensions of the fin are one quarter to one half a wavelength deep at a point half way along its length and one or two wavelengths in maximum peripheral measurement away from the surface at the frequency of operation, a notch is disposed in the fin substantially half-way along its length and a transmission line connected across the notch for coupling the fin to a transducer. The aerial is of particular use on aircraft, the fin being arranged to lie along the direction of flight and the surface being the aircraft skin. Preferably the fin is mounted at right angles to the surface and in its simplest form, Fig. 1 (not shown), consists of two flat laminµ a quarterwavelength square attached to the conductive surface in the same plane so that there is a gap or notch between them. A coaxial feeder brought through a hole in the surface adjacent to one of the laminae has its outer connected to the one lamina and its inner conductor to the other. The position of attachment of the feeder along the length of the notch if chosen to match the aerial to the feeder and the width of the notch is made small compared with the operating wavelength and preferably such that the characteristic impedance of the notch regarded as a transmission line approximates to the radiation resistance of the aerial. The simple laminµ may be replaced by streamlined and hollow members such as a<SP>1</SP> and b<SP>1</SP> (Fig. 2) concealing and protecting the transmission line d. Two parasitic fins el and e<SP>2</SP>, tuned by notches c<SP>1</SP> and c<SP>2</SP>, may be disposed parallel to the aerial and so dimensioned that the currents in them lead or lag those in the aerial as required. Each parasitic fin may be regarded as approximately equivalent to a dipole coincident with the edge of the fin remote from the surface. In an end-on array a simple aerial system a2, b<SP>2</SP> fed across the notch c is extended by additional portions a<SP>3</SP> and b<SP>3</SP> of about the same dimensions as, and respectively coupled by notches c<SP>3</SP> and c<SP>4</SP> to, a2 and b<SP>2</SP>.