An investigation and application of the contrawound helix

An investigation of the contrawound helix and the determination of its characteristics has been completed. By means of a hollow-beam traveling-wave tube and perturbation methods, the fundamental and minus-one space harmonics impedances have been measured and a number of space harmonics of the symmetric and antisymmetric modes identified. The fundamental impedance was measured to be equal or greater than the sheath-helix impedance depending, however, upon the thickness and width of the helix tape. The minus-one space harmonic impedance was measured to be larger than the fundamental impedance for ka > 0.65. The contrawound helix has been employed as a high-power X-band amplifier (8.5-9.5 kmc). The characteristics of the tube described are 25-db gain, power out > 1 kw, efficiency 7-10 per cent.