Normal Mode Bends for Circular Electric Waves

In dielectric-coated round waveguide the degeneracy or equality of phase constants of TE01and TM11waves is removed. In such a non-degenerate waveguide, mode conversion in bends can be reduced by changing the curvature gradually instead of abruptly. With curvature tapers, which are of the order of, or longer than, the largest beat wavelength between TE01and any of the coupled waves, propagation of only one normal mode is maintained throughout the bend. Linear curvature tapers can easily be made by bending the pipe within the limit of elastic deformation. Changes in the direction of a waveguide line can thus be made by inserting a dielectric-coated guide section which is elastically bent over a fixed center point. A thirty degree change of direction of a 2-inch I.D. pipe with 30 ft of a dielectric-coated guide yields a total bend loss at 5.4-mm wavelength that is twice the TE01loss in 30 ft of straight pipe. An optimum bend geometry is found which minimizes the total bend loss. The normal mode bend is a broadband device