The widely accepted manner of evaluat in g t he quality of coaxia l radio-freque ncy connectors was in the past limited to a single case, namely, to the condition when t he load terminating t he syste m was equal to t he characteristic impedance of t he li ne on the output eJld of t he connector. The quality was exp ressed as the voltage stan d ing-wave ratio in t he input line.To broaden this method of e valuat ion a "co nnector " is redefined, and seve ral methods are given to find t he correct ions of various types of connectors wi t h any terminat ion. Typical results of measureme nts made by t hese methods are give n for frequencies from 100 to 900 megacycles. Application of t h ese me thods are also indicated in determining t he quality of t ransm issio n lines in ge ne ral.
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I. INTRODUCTIONCCURACIES of impedance measurements in waveguide of coaxial cross section have been improved by a factor of ten in less than two decades, an achievement based primarily on the parallel development of precision coaxial-line standards and precision coaxial connectors.' The development of these coaxial-line standards and their contribution toward improved impedancemeasurement systems will be reviewed in this paper. Improvements in bridge, slotted-line, and reflectometer measurement techniques that have taken place during this same period would not have been accomplished without concurrent improvements in precision connectors. These connectors have extremely low VSWR's and provide well defined reference planes.To give some background on the early development of coaxial impedance measurements, the basic methods and techniques will be mentioned. These start with the method of measuring impedances by the use of slotted lines [ 1 ]- [3]. A single fixed probe can also be used by separating the probe from the load by a length of line containing a variable phase shifter allowing one to observe the standing-wave pattern [4] as it sweeps past the probe. Reflectometer systems using directional couplers [5] and hybrid junctions [ 6 ] , operated at a single frequency, provide a way to measure the amplitude of reflection coefficient, but often without information about relative phases of the two traveling waves. Reflectometers operating at single frequencies are described by Beatty [7]. New methods employing swept-frequency techniques, described by Ely [54], can be used to obtain the amplitude and the phase of microwave parameters.
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