Minimum Loss Condition of a Bent Rectangular Tube Waveguide

The leakage loss of a tube dielectric waveguide is analyzed analytically and numerically. A minimum loss condition of a bent rectangular tube waveguide is derived in terms of the ratio of refractive index of the tube to the other region using the transverse transmission-line model. The validity of the derived minimum loss condition is confirmed by the two- and three-dimensional beam-propagation methods.