Patent GB-517935-A (GB)
Title: Improvements in or relating to systems for transmitting high frequency electric waves
IPC: H01P1/201
Filed: 1938-08-10
Abstract: 517,935. Transmission systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 10, 1938, No. 23600. Convention date, Sept. 8, 1937. [Class 40 (iv)J (Also in Group XL] In a system in which high-frequency currents are transmitted along a line, a network, preferably of the Lecher-wire type, is asymmetrically coupled to the line so as to induce or to suppress standing waves, preferably by affecting waves in one direction differently from those in the other. In a transmission line 102, Fig. 8, connecting a source 101 of oscillations with a load 103, the effect of mismatching of the load is neutralized, so that standing waves are suppressed between the load 103 and a point in the line, by means of a coupled network N comprising a quarter-wavelength line, or resonator, half 105 of which is parallel and adjacent to the main line while its other half 106 is vertical. The Specification contains a mathematical discussion which enables the optimum conditions to be chosen and leads to the results shown graphically in Figs. 8A, 8B, where q is the ratio of the current at antinodes to the current at nodes of the standing waves, and P is the distance, measured in electrical degrees, at a given wave-length, by which the nodes and antinodes are shifted when a specified change is made in the ratio of reactance to effective resistance in the coupled resonator N, while 1 is the length in electrical degrees of the coupled section 105 of the resonator. When, for instance, a mismatched load 103 such as an antenna has to be compensated, the ratio q is first measured on the mismatched line by means of a slide-wire meter or otherwise, a curve capable of giving the ascertained value of q is selected from Fig. 8A, where the curves 1, 2 correspond to different coefficients of coupling between the resonator N and line. 102, these coefficients being determined by the distances apart of the wires ; thus the length 1 of the resonator N and its distance from the line 102 can be chosen by the aid of Fig. 8A. The distance P between the conductors 106 of the resonator and a current node, whose position has been ascertained by means of the slide-wire meter, is then determined by the aid of Fig. 8B, in which curves 5, 6 correspond to different coefficients of coupling. Errors due to end effects and the like are compensated by adjusting the position of the short-circuiting bar 107. The theory'is discussed in connection with a straight quarterwave resonator such as 905, 906, Fig. 22, with reference to Figs. 4A to 7 (not shown) ; preferably, a large coupling coefficient is chosen. If several different frequencies are simultaneously transmitted, several corresponding resonators N are coupled to the line and are so chosen that each suppresses standing waves at its own frequency which exerting a negligible effect at the other frequencies, Fig. 21 (not shown), the requisite conditions being discussed in the Specification, and in extreme cases the resonator N may have to be constructed of wire or copper tube having a large diameter. In a modification; Figs. 9, 9A (not shown), the horizontal part 105, Fig. 8, is #/4 long, where # is the wave-length, and at each end of this part there is a vertical extension 106 #/8 long, the short-circuit being applied to the lower end of each extension. In further modifications, Figs. 10, 11, 13 (not shown), the position of one or more. short-circuits 107 and the lengths of the conductors are variously chosen. The part 106 may be oblique instead of vertical, Fig. 12 (not shown) ; three short-circuited pairs of conductors may be connected to form a tee; Fig. 14 (not shown) ; the short-circuited conductors may be extended if a short-circuit is added at every current node, and the resonator may in effect be shifted in that case by shifting the short-circuiting bars and vertical portion along fixed wires 105. - The Specification indicates that the electrostatic field of the line is effective upon the resonator at short circuits or bends, while that of the resonator is effective upon the line near open ends or bends; but a pair of straight detached conductors, Fig. 15 (not shown), may produce the desired effect if they are suitably located near a bend in the line. In a further modification, Fig. 16, the resonator is short-circuited at both ends, but in order that its reactance may not be unduly high its length has to be n#/2, wherefore the electrical path along the line has to be lengthened by means of loops 1602, in order that the e.m.fs. induced in the shortcircuits 1607, 1608 may not cancel each other. Alternatively the limbs of the line may be interrupted by insulators and cross-connected in order to secure the requisite asymmetry, Fig. 17 (not shown). The invention may be applied to coaxial conductors such as 1801, 1802, Fig. 18, where inner conductors 1803, 1806 are coupled by juxtaposition; alternatively, the portion 1803 may be omitted and the portion 1806 may be continued so as to run partly parallel to the main inner conductor 1802, Fig. 19 (not shown). The invention may be applied to a single-wire line with earth return, Figs. 1, 2, 3, 20 (not shown). Phase-shifting systems.-If waves 907 are travelling without reflection from a source 902 to a load 904, Fig. 22, their phase may be shifted by means of two resonators 905, 906, coupled to the line. The first introduces reflections which result in standing waves 908, and the second elminiates the standing waves over the remainder of the line. The phase of the travelling waves 909 is adjusted by shifting the relative positions of the resonators 905, 906. Tuned couplings.-A source 2408, Fig. 24, of oscillations is connected through a line 2409 to the resonator 2406, the impedances of the line and resonator being matched by suitable choice of the length of the resonator and the points of connection. The load Zo terminating the main transmission line 2401 is matched so that forward waves F, induced in the line 240,1 by the source 2408 through the resonator 2406 are not reflected, whereas backward waves B are reflected at the shortcircuit 2403, so that the phase-difference between the two waves can be adjusted' by moving' the short-circuit; in this way the effective transfer coefficient between the resonator 2406 and the line 2401 can be varied, becoming, for a given wave-length, zero when the forward waves F and the reflected waves are in phase opposition and a manimum when these waves are in phase. The source 2408 may be replaced by a receiver, a source of oscillations being associated with the terminal impedance Zo, Fig. 25 (not shown).