Waveguide structures for low-loss transmission around sharp bends in circular waveguide

Insertion-loss measurements over the frequency band from 28 to 39 Gc/s have been made on a number of curved waveguide structures of circular cross-section. These included a waveguide periodically loaded with both tapered and parallel-sided dielectric discs placed transversely, in addition to longitudinally and circumferentially corrugated waveguide. It was found that the inhomogeneous anisotropic dielectric loading was difficult to fabricate accurately. Dielectric losses limit the usefulness of this method. Longitudinal corrugations of the wall of the tube were used to provide an anisotropic surface reactance and so break the TE01-TM11 mode degeneracy. It was found, unfortunately, that the attenuation coefficient of extruded waveguide of this kind in straight lengths was excessive. Circumferentially corrugated waveguide was also used to remove the TE01-TM11 mode degeneracy with much more success. Provided that the waveguide is not too highly overmoded, such a structure gives a method of negotiating a sharp bend with low loss.