GB882997A - Improvements in electrical delay lines - Google Patents

Abstract

882,997. Travelling wave tubes. MULLARD Ltd. Feb. 27, 1958, No. 6384/58. Class 39(1) [Also in Group XXII] The interdigital delay line of a travelling wave tube is made by taking grid wires 1, Fig. 1, which are flat or substantially flat and which are provided with two longitudinal parallel backbones 2, the wires then being bent to hairpin form round a preferably grooved mandrel 5, Fig. 4, and the backbones 2 clamped between a pair of supports 7 (which may form parts of a waveguide) by releasable securing means such as bolts 8 two sets of such hairpin elements being assembled to form an interdigital line. The backbones which are metal strips 2 are arranged in a circle and adjacent ones are inclined in opposite directions to a radius, the grid wire being wound in grooves in the backbones when a mandrel carrying the backbones in recesses therein is rotated by a shaft. After removal from the mandrel the wires are attached to the backbones. The wires are severed at the mid points between alternate backbones so as to leave wire lengths extending between backbones 2a and the free ends are trimmed off. After removal from the mandrel 3 and clamping to the mandrel 5 the wires are attached to the backbones by brazing the wires to the backbone grooves or by swaging the grooves over the wire and the backbones are brazed to each other. The wires are straightened by moving the backbones in opposite directions until the wires extend at right angles to the backbones. The grids are then stretched to set them. The grid wires are then bent over the curved edge of the mandrel 5 to hairpin shape; the mandrel 5 preferably but not necessarily has grooves at 6 to take the grid wires. The recesses or grooves in 2 are -inclined at 45 degrees as shown in Fig. 4, and bending the wires over the mandrel brings the backbones 2 into contact with one another. The hairpin structure is clamped to mandrel 5 and the assembly is secured between two blocks 7 by bolts or other threaded members 8. The clamp holding the wires 1 to the mandrel 5 is now removed and the mandrel 5 leached out by solvent. The two sets of hairpins each hairpin being carried by an individual pair of backbones 2 are now interleaved and clamped together by bolts to form an interdigital delay line. In a modification the mandrel may be leached out before the structure is bolted together between blocks 7. After bending the wires into loops the backbones are brought into contact with a different surface of the mandrel and the mandrel with the looped wires thereon is put between two metal blocks. The two backbones can if desired be additionally secured together by fusion of metal.