Patent GB-852002-A (GB)
Title: Improvements in and relating to electrical delay lines
Inventor: FROOM JOCELYN
IPC: H01J23/28
Filed: 1957-06-20
Abstract: 852,002. Travelling wave tubes. MULLARD Ltd. Feb. 19, 1958 [June 20, 1957], No. 19446/57. Class 39(1). [Also in Group XXII] A delay line comprises two interdigitally disposed linear assemblies of evenly spaced wire hairpins, the ends of each hairpin being respectively secured to two parallel rods 1, Fig. 4, and the two rods 1 are held in spaced relationship within respective recesses in support members 5 extending along the assembly. The support members 5 may form parts of a hollow pipe waveguide. In manufacture two grids of flat or substantially flat form are each bent around their longitudinal centre lines to form the hairpins. In assembly molybdenum wire is wound on a mandrel round two backbones in grooves therein, the grooves being formed during the winding by the winding machine, the slots being subsequently brazed or swaged over, the grid wires on one side being removed after the swaging or brazing. (The wires are preliminary plated with gold then brazed to the grooves, if brazing is adopted) to put the legs of each hairpin in the same transverse line, the backbones are displaced in opposite directions relatively to one another after which the grid is stretched to consolidate the position of the grid wires. The grid wires are now placed over and in the grooves of a mandrel 3, Fig. 4, and the grid wires are stretched to consolidate their position with respect to the mandrel. The mandrel and wire hairpins thereon are now placed between two copper blocks 5, Fig. 4, having recesses for the reception of the backbones 1 and the blocks are previously gold plated to facilitate brazing them together after the mandrel has been inserted therein. the backbones and hairpins also being swaged or breezed in position at the same time. The mandrel is now removed by dissolving or backing out by a solvent. The other half of the delay line is made in the same manner as the first half and the two halves are brought together to interleave. Copper spacing bars ensure the desired degree of interleaving of the two sets of hairpins and the assembly is finally bolted together. In the modification of Fig. 7 the grid wire is wound on a cylindrical mandrel the backbones 1 being replaced by wires 7 partially recessed into the surface of the mandrel and the wire 2 is wound thereover. The outer surfaces of the wires 7 are grooved for reception of the wires as wound, the grooves being subsequently swaged over to hold the wires in position and further secured by fusion of metal if desired. The wires are cut at points midway between the closely adjacent support wires and the ends trimmed off. The larger the diameter of the mandrel the less the inclination of the grid wires so that less subsequent straightening of the grid wires is necessary. The mandrel surface may be planed flat so that the wire does not contact the mandrel. There is also described a form similar to Figs. 1-6 (not shown), in which the backbones are replaced by wires and the grid wires are stretched only once (on the mandrel 3). In another form a double sided grid is wound with one side at right angles to the side members and the other side wound diagonally, the diagonally wound grid wires being finally removed.