Waveguide Bending Design Analysis: Theory of Bending and Formulae for Determination of Wall Thicknesses

For many years, waveguide bends for most microwave installations have been difficult and expensive to produce. The art of tube bending was not sufficiently advanced to make economically possible the extremely close tolerances required in waveguides. This was true even when waveguides were first introduced into radar equipment. It later became evident, as increased power, higher aircraft speeds and missile applications made waveguide requirements more severe, that the bending technique would have to be improved. First, a faster method of bending had to be found, since the best of existing methods required about 30 minutes to make one bend. Second, to reduce transmission losses, the new method had to produce bends that met closer internal cross-sectional tolerances. Third, bends of much smaller radius, more closely spaced compound bends and bends adjacent to swaged and twisted sections had to be made to meet new design demands. In addition to these specific improvements and innovations in the bending technique, production uniformity was desirable, since it is only through uniformity that statistical quality control can be realized. At the Western Electric North Carolina Works the development of waveguide bending began in 1951 and continued for the next five years. This article describes the new bending process and indicates how internal cross-sectional accuracy is maintained despite material flow due to the bending action that changes the tubing's external dimensions. This in1457