Cylindrical waveguide as a power transmission medium—Limitations due to mode conversion

A cylindrical waveguide operating in the TE01mode can transmit powers of the order of thousands of megawatts in frequency ranges below 10 Gc/s with acceptable copper losses over distances of hundreds of miles, provided it can be made with sufficient accuracy to avoid excessive power transfer into other unwanted high-loss modes. The tolerances on the guide straightness appear to be the most severe limitation on the use of this type of guide as a high power system component. These tolerances are evaluated here and found to be of the order of 10 to 100 mils in distances of a few hundred feet for typical values of the other parameters such as 1.0 Gc/s in a 2-meter-diameter guide providing 1 dB power loss in a distance of 200 miles. Tolerances on diameter variations and cross-section ellipticity are also evaluated and found to be of the same order of magnitude as the deviations from straightness, but should be easier to control by the proper manufacturing process. It is also shown that low loss bends (about 0.01 dB/mile) with bending radii of the order of 0.5 mile are possible if the length of the bend is accurately controlled and the guide has a dielectric lining of the proper thickness.