In this paper a newly developed helieal coordinates is used to make out the solution of electromagetic fields in the helix gap and calculate dispersion characteristics of tape helix slow wave structure for the first time. Strict boundary conditions for magnetic fields are adopted and are treated rigorouSly by Fourier expansion. boldes

the radial propagation constant of every layer in the dielectric-loaded region is differentiated. Some of practical tape helix slow wave structures have been calculated for dispersion characteristics and the calculated values accord with measured values very well. The authors also compare the calculated results with experiments for different structures by changing tape thickness or other structure parameters and find that the theory in the paper is universal.