A Technique for Measuring the Efficiency of Waveguide-to-Coaxial-Line Adaptors

This paper describes a technique for measuring the efficiency of a waveguide to coaxial line adaptor fitted with a sexless connector. Three such adaptors of the same type are required to implement the technique but there are no constraints on the characteristics of the individual adaptors; neither low dissipative attenuation nor low VSWR are necessary and identical performance of adaptors within the set of three is not assumed. Any error in the adaptor evaluation due to modes other than the principal mode propagating between "back-to-back" adaptors can be detected and eliminated. A method is described for quantifying the uncertainty in adaptor efficiency in terms of component uncertainties in the evaluation and the results obtained with three WG16 (WR90) to GR900 adaptors at 8.2 GHz are used to illustrate the technique. Although dependent on the reflection coefficient terminating the adaptor, typical 95-percent confidence limits for an adaptor efficiency of 99 percent vary from ±0.08 to ±0.12 percent. The technique is also applicable to adaptors between waveguides of different cross-sections, e.g., circular to rectangular or taper sections, and also to sexless coaxial to coaxial adaptors.