WT4 Millimeter Waveguide System: Mechanical Gauging Techniques

During the development of the WT4 waveguide system, mechanical measurements of the various geometric distortions in the waveguide were used extensively To monitor the manufacturing processes to ensure conformity to the specification. To correlate mechanical distortions in the waveguide and the field evaluation test line with electrical loss measurements to improve manufacturing processes and installation techniques. To acquire a better theoretical understanding of the relationship between mechanical distortions and electrical loss. In many cases mechanical measurements are of greater value than direct electrical measurements. The problems associated with making accurate electrical measurements on long waveguide runs at millimeter wave frequencies are well known1; those of attempting to measure di2007 rectly the mode conversion loss in a single section of steel waveguide tubing are better imagined! In fact, even if such measurements could be made, they would still be of limited utility in that they usually could not identify the cause of loss but only indicate its presence. To see this problem in the proper perspective it should be remembered that in the WT4 waveguide system a serious distortion 2 which results in losses of 0.1 dB/km corresponds to a single tube loss of 0.001 dB. Consequently measurements of most of the individual loss components on a single tube require accuracies on the order of 10~5 dB. Electrical measurements of this accuracy are currently impossible in the 40 to 110 GHz band.