An automatic bridge for measurements on loss-free waveguide junctions

The experimental curves required in the Weissfloch or Feenberg method for measuring the parameters of a loss-free waveguide junction may be obtained by using a bridge in which the essential component is a magic-T. An analysis of the performance of the bridge shows that accurate results can be achieved provided that the isolation between one pair of arms of the magic-T exceeds 44dB. This analysis also leads to a simple technique for measuring the isolation between a pair of arms. Methods by which feedback may be applied to the bridge to give automatic operation are described, and details are given of two such methods which have been found to give satisfactory performance.