  A generic problem of high frequency wave propagation along a metallic strip
in parallel above a PEC ground plane is considered. The wave is excited by an
elemental electric dipole at an arbitrary location above the PEC plane. The
full wave problem, for arbitrary widths of the strip, is solved by means of a
mode matching approach and expansion of the strip surface current into
Chebyshev polynomials. For narrow strips, an approximate method using only
longitudinal currents is derived, and compared numerically with the full wave
method. Utilizing the concept of equivalent radius, the approximate method for
narrow strips is evaluated numerically against results for thin circular wires.
It is concluded that the approximate method is suitable for handling multiple
wires in layered structures, wherefore the method has potential usefulness for
estimating long range propagation of high frequency waves in wire structures
like power lines and railway feeding systems, containing over-head wires and
wires submerged into ground.
