GB654707A - Improvements in or relating to radio aerials for aircraft - Google Patents

Abstract

654,707. Aerials; multiplex radio signalling. MINISTER OF SUPPLY. July 2, 1948, No. 17911. [Classes 40 (v) and 40 (vii)] In order to provide a vertically-polarized omni-directional multi-waveband suppressed aerial system for an aircraft having a metallic or metallized fabric skin, the tail fin is formed with a conductive tip portion 2, Fig. 2, separated from the conductive body portion 4 by an insulating member 3, the inner and outer conductors of a coaxial feeder being connected to portions 2 and 4 respectively and the relative dimensions of the two portions being chosen so that when excited in any one of thiee contiguous frequency bands in the H.F. or V.H.F. range, the tip operates alternatively as (1) a near-end feed to the aircraft acting integrally as a radiator, (2) as a near-end feed to the body 4 of the tail fin with the tail plane acting as a counterpoise earth, and (3) as a resonant unipole radiator with the body 4 of the tail fin acting as a counterpoise. In all three modes of operation the effective width to length ratio of the aerial is large and the frequency bands are therefore wide. The aerial system may be operated in the three modes simultaneously by employing three feeders containing appropriate frequency filters, two such feeders being shown in Fig. 2. In a modification, Fig. 3, the conductive tip comprises a number of separate metallic portions 7, 8, 9 and 10 mounted on an insulating plastic support 6, the lowest portion 7 being operable in the three modes described above and each of the other three portions being operable in a different frequency band as a resonant omni-directional unipole with the adjacent lower portion acting as a counterpoise earth. Alternatively, the portions 8, 9 and 10 may be replaced by a small telescopic aerial which may be adjusted for operation in a selected band within a predetermined wider band. A method of feeding a five waveband triple-tip system is shown in Fig. 6 in which the lowest portion 21 is fed by three coaxial feeders 25, 28 and 31 whose outer conductors are connected to the conducting skin of the aircraft at points 25a, 28a and 31a. The upper portion 23 functions as a resonant unipole with the middle portion 22 as its counterpoise, the two portions being connected respectively to the inner and outer conductors of coaxial feeder 35 and the portion 22 also functions as a resonant unipole with portion 21 as its counterpoise, portion 22 being directly connected to the inner conductor of coaxial feeder 33 and a low-impedance path being provided between portion 21 and the outer conductor of feeder 33 by means of a suitable filter in one of feeders 25, 28 or 31.