GB472725A - Impedance matching terminations for dielectric guides - Google Patents

Abstract

472,725. Signalling through dielectric guides. STANDARD TELEPHONES & CABLES, Ltd. (Western Electric Co., Inc.) Oct. 2, 1936, No. 26785. [Class 40 (v)] Relates to dielectric transmission lines for carrying high-frequency energy in the form of waves, which may be variously polarized. The invention consists in the use of absorbing or reflecting elements so arranged in relation to the guide as to produce a desired terminal impedance, or transformation effect. As shown in Fig. 9, a wave travelling along the guide 101 from the left is partly reflected, partly absorbed, and partly transmitted by radial resistance wires 107 which are connected by an axial conductor 103 to an adjustable plunger 102. The transmitted energy is totally reflected from the face of an adjustable metal plunger 102, and the wave may subsequently be completely absorbed by successive interaction between the wires 107 and the plunger 102. The wires 107 may be replaced by a single resistance wire, or by a highly-conducting wire with a " lumped " resistance, in association with crystal rectifiers or thermo-electric couples, to detect the signal currents as shown in Fig. 13. Fig. 15 shows a method of introducing an impedance transformation. The main " guide " 108 opens through an iris diaphragm 109 into a cross-chamber 110 which is closed at both ends by adjustable pistons 102 and 102<1>. The element 106 may be an absorbing disc or a resistive conductor. For a given position of the inlet 108, and a given distance between the pistons 102 and 102<1>, a standing-wave system is set up, as shown by the curve ABC, inside the cross-chamber, and its amplitude can be controlled., to secure a step-up or step-down effect, by altering the relative dispositions of the movable parts. Certain settings are found to be critical, and can therefore be used to give high selectivity. In Fig. 20, antenna members 127 pick up waves from the upper guide and transfer them through the impedance-matching Lecher-wire coupling 121 to similar members 127<1> in the lower guide, which has a different diameter from the first. The absorbing elements may be mounted externally to, or in, or associated with the walls of the dielectric guide. They may also be arranged to ensure the maximum transfer of energy to the guide from an oscillating source. In Fig. 33, resistance films 51, 52, 53, spaced apart by dielectric material 56, are used to absorb waves of different selected polarities and different frequencies. Various modified arrangements suitable for this purpose are also described. Fig. 55 shows how lateral branches 83, 831 and 84, 84<1>, of suitable diameters, can be arranged to separate out waves of different polarity, and of different frequency from those flowing along the main guide 54.