Patent GB-743228-A (GB)
Title: Improvements in or relating to aerials and to impedance matching devices
Inventor: CHARMAN FREDERICK JOHN HENRY
IPC: H01Q11/04
Filed: 1953-07-08
Abstract: 743,228. Aerials. ELECTRIC & MUSICAL INDUSTRIES, Ltd. July 1, 1954 [July 8, 1953], No. 18885/53. Class 40 (7). A travelling wave aerial comprises a length of coaxial cable, means being provided at the end opposite to that to be connected to a transducer for feeding current between the outer and inner conductors. Various means are described. In one the inner conductor 3 of the cable 1 is extended a length of approximately a quarter wavelength beyond the inner conductor 2 (Fig. 1, not shown). In another a quarterwavelength long sleeve is spaced from and surrounds the end of the outer conductor and is connected to the inner conductor, (Fig. 2, not shown). In a third a conductor 8 approximately a quarter-wavelength long is placed alongisde and preferably parallel to the end of the outer 2 and connected to the inner 3. In each case the characteristic impedance of the coupling means should be the geometric mean of the impedance of the outer surface of the cable and of the inner conductor. The aerial may be formed by extending the length of coaxial feeder coupling the aerial to the transducer and the actual length of the cable forming the travelling wave aerial defined by providing a quarter-wave rejector sleeve at the appropriate point on the feeder. In an alternative form the rejector may consist of a quarter wavelength conductor 11 parallel to and connected to the outside of the cable as shown. The outer conductor 2 is preferably earthed as for example by means of an artificial earth consisting of a coiled half wavelength of wire 12 attached by its centre point to the outer conductor 2 through a resistance 13 of a value equal to the characteristic impedance of the conductor 2; at high frequencies the stray shunt reactance across the resistance may be tuned out by the provision of an inductance 14. The invention may be applied to a V-aerial (Fig. 4), each arm of the V being a coaxial line terminated in one of the coupling means described. The ends at the apex of the V are arranged parallel to each other for a quarter wavelength and then joined as shown to form a two-wire balanced screened line. The parallel portions are each arranged to have a characteristic impedance such as to match the impedance of the aerial to that of the transmission line and they also form a rejector presenting a high impedance at the apex of the V; a terminating resistor 19 may be connected across the arms at this point. An open wire transmission line may be used in place of a screened one. A rhombic aerial is shown in Fig. 5; the feeder arrangement is similar to that of the V- aerial just described and the distant end is provided with the cross connected quarter wavelength coupling means indicated. One half of this arrangement may be made in the form of a single conductor, a single crossconnection only being used. The faces of the connecting elements used have been described as parallel but may be closer together at one end than the other; suitable arrangements of this type producing a wide-band aerial. The aerials are in any case effective at the frequency where the length of the coupling means is 3#/4 and may also be used as a resonant aerial. Specification 493,758 is referred to.