The Observed 33 to 90 kmc Attenuation of Two-Inch Improved Waveguide

The conditions favorable for low TE 0 i transmission loss in waveguide occur when the operating frequency is remote from cutoff and many other modes can consequently coexist. Two-inch inside diameter copper pipe can, for example, propagate 80 modes at 33 kmc, nearly 300 modes at 60 kmc, and about 700 modes at 90 kmc. When so many modes can be propagated, the presence of imperfections in the waveguide will introduce coupling between the TEoi and other modes. The spurious modes which are excited at such imperfections increase the TE 0 i loss, and a distribution of such imperfections can produce mode conversion-reconversion e f f e c t s ' w h i c h cause the TEoi loss to fluctuate in an unpredictable manner with frequency. Imperfections which occur in a long line can be divided into two categories: joints between sections and imperfections in the pipe itself. Discontinuities at the joint comprise tilt, offset, and change in diameter. The imperfections of the pipe are of a more distributed nature and comprise changes in diameter, ellipticity, and the more or less random deviations of the axis from a straight line. It has been shown by experience that with 1323