Propagation around bends in waveguides

When a waveguide supporting a given mode is bent at some point along its length, there is generally a problem in providing for the continuity of the same undisturbed field pattern throughout. The hollow metal rectangular waveguide transmitting the dominant H01 mode and bent in the E-plane is an exception to this, but for the most part mode conversion occurs at the bend, which can have serious consequences in multi-mode tubular waveguides or in surface waveguides. To minimize this difficulty in the circular Hoi waveguide, a proposal was made previously to use an inhomogeneous dielectric in association with the waveguide as a means of accelerating the wave pattern on the outside of the bend and retarding it on the inside, so as to approach much more closely the ideal conditions. In the present paper this idea has been extended to other forms of waveguide, and dielectrics which might find application in this way are briefly discussed.