The dispersion equation for a planar traveling wave tube with anisotropically conducting open helix structure is derived. Using, the accurate boundary conditions along all the sides of the planar TWT and along the winding direction of the TWT using indicator function, the exact solution of a homogenous boundary value problem for Maxwell's equations is derived. A total number of six different complex constants are derived from a set of six boundary conditions for the proposed cold wave analysis. The presented theoretical analysis will be used in the design of the planar travelling wave tube amplifier (TWTA). © 2019 IEEE.