Patent GB-572881-A (GB)
Title: Improvements in or relating to high frequency electric transmission lines and wave guides
IPC: G01R21/04
Filed: 1943-09-14
Abstract: 572,881. Wave guides. COLLARD, J. Sept. 14, 1943, No. 15089. [Class 40 (v)] [Also in Group XXXVI] A wave guide, or the outer conductor of a coaxial line, has the whole or part of its surface formed of a plurality of closely-spaced conductors arranged to simulate a continuous conductive surface for desired wave energy. The conductors may be of material with high temperature coefficient of resistance, and a meter indicating this change of resistance may be used for measuring the power passing through the guide or line. In Fig. 1, the rectangular guide has windows 6 in opposed walls 4, 5 across which parallel insulated wires 8 are stretched to form a grid. The wires are in a continuous length and their outer parts lie against flanges 7 formed on the guide, these outer parts being of a length equal to one quarter, or an odd number of quarters, of the wave-length. As these quarter-wave lines are open at their outer ends, they present the equivalent of a short-circuit at their inner ends. Thus, for the desired wavelength and for waves of the desired mode, the grid acts as a continuous conductive surface, whilst undesired waves and direct current are attenuated or eliminated. The power passing in the guide is measured by using a wire 8 of suitable metal and connecting it to a bridge circuit for measuring its resistance. A second arm of the bridge may be formed of a wire similar to the wire 8 and subject to similar ambient temperature, for 'balancing out the effects of changes in ambient temperature. The wire 8 may be replaced by a sheet of insulating material, Fig. 3, coated on one side with a film of suitable metal, e.g. platinum. The film is cut away along the lines 9 which overlap at the area occupied by the window 6 when the insulating sheet and film are placed in position adjacent the flanges 7 of the guide. For use with a coaxial line, the wires 8 stretch across windows placed at diametrically-opposite areas of the outer conductor, and are arranged to lie in an axial direction. The quarter-wave portions of the wire lie against flanges formed in planes transverse to the axis at opposite ends of each window (Fig. 4, not shown). For a circular wave guide, Fig. 5, the grid is formed as a cylindrical helix of metal tape 28 with a narrow edge of the tape facing the axis of the guide. The grid is interposed between flanges 27 formed on the wave guide sections 21, 22, and the spaces between the turns of the helix are occupied by solid dielectric 29. The width of the tape is such that quarter-wave lines extending in a radial direction are formed between adjacent turns of the helix and between the end turns and the flanges 27. In a further modification, the tape extends to and fro in an axial direction as shown in Fig. 6. Means may be provided for short-circuiting some or all of the outer edges of the tape 28, Figs. 5 and 6, so as to interrupt wave transmission through the guide. Fig. 8 shows a guide 31 which may be formed of flexible insulating material, such as rubber, with a large number of short wires thrust through holes 32 in the walls so as to provide quarter-wave lines with an open circuit at their outer ends. To waves passing along the guide, the wires appear to be short-circuited at their inner ends and are equivalent to a continuous conducting surface. The guide 31 may be a solid instead of a hollow rod. The wires or conductors may alternatively be of a length equal to one half-wave, or a number of half-waves, and are then short-circuited at their outer ends.