Attenuation of the TE01 wave within the curved helix waveguide

The change in the field pattern of the TE01 mode in the helix waveguide with constant curvature is calculated by means of a perturbation method. The helix waveguide has a coating of a lossy dielectric and is shielded by a metallic pipe. By bending this waveguide, the original field pattern of the TE01 wave is slightly perturbed. The perturbation produces additional field components which give rise to an electromagnetic field in the lossy dielectric. This field causes energy dissipation and gives rise to an additional attenuation. In this paper formulae for the curvature attenuation caused by the dielectric losses are given. It is shown that the attenuation due to curvature can be remarkably reduced by proper choice of the thickness of the dielectric layer between helix and metallic shield.