Improvements in or relating to matched terminations for wave guides and coaxial lines

摘要

732,683. Matched terminations for waveguides &c. DECCA RECORD CO., Ltd. June 15, 1953 [June 16, 1952], No. 15166/52. Class 40 (8). A matched termination for a wave-guide or coaxial line comprises two or more resistive elements 12, 13 spaced apart approximately #/4 in the guide or line, and a short-circuit 11 beyond the elements 12, 13. The elements may comprise strips of, e.g., graphite on a dielectric base or evaporated nickel-chromium alloy films on thin glass vanes. The strips may be slid into the guide through slots preferably in its narrow walls so that the amount of the coated material in the guide may be adjusted. This construction overcomes the difficulty of producing strips of known and constant resistivity. Due to the gaps between the strips and the broad walls of the guide and the effect of the dielectric base of the strips a capacitive effect is set up which is compensated for by slightly reducing the spacings l 1 and l 2 from #/4 to e.g. 0.9 #/4. An expression is given for calculating this distance. Expressions are given for calculating the magnitudes y 1 SP1/SP, y 2 SP1/SP of the shunt conductances of the elements 12, 13. y 1 SP1/SP=¢ and y 2 SP1/SP=2 for minimum variation of the resistive component, and y 1 SP1/SP=0.293 and y 2 SP1/SP=1.414 for minimum variation of the reactive component. As the magnitude of the reactive variations are greater than the resistive variations, y 2 SP1/SP and y 1 SP1/SP are usually given values nearer 1.414 and 0.293. For a coaxial line, the elements are connected between the inner and outer conductors.