Propagation of electromagnetic waves guided by an open tape helix

The dispersion equation for free electromagnetic waves guided by an anisotropically conducting open tape helix is derived from the exact solution of a homogenous boundary value problem for Maxwell's equations without invoking any a priori assumption about the tape-current distribution. The approximate dispersion curve tends to be close to the dominant-mode sheath-helix dispersion curve in the middle portion of first two allowed regions exhibiting a marked downward deviation everywhere from the sheath-helix dispersion curve in the third allowed region. The dispersion curve tends to slope downward towards the forbidden-region boundaries in all the three allowed regions. The magnitude plot of the current distribution on the tape surface exhibits a maximum along the center line of the tape irrespective of the width of the tape. The phase of the surface current distribution on the other hand exhibits a nearly linear variation across the entire width of the tape.