Coordinate transformation in the study of tape helix
带状螺旋线研究中的坐标变换

The Floquet form of electromagnetic field in travelling wave tubes with tape helix is analyzed in the cylindrical coordinates frame. The study showed that appropriate coordinate transformation is the sufficient condition for separation of variables of electromagnetic field. The separation of variables under the coordinate transformation is the basis of the theory in which the assumption about the surface current density distribution of the tape is avoided. The dispersion and coupling impedance of a typical structure are calculated. The computed and measured results agree with high accuracy.