Ray-optical prediction of radio-wave propagation characteristics in tunnel environments-Part 1 : theory

Abstract

A tunnel is modeled as congregates of walls, with

the wall being approximated by uniform impedance surface. The

aim is to get a solution for a canonical problem of a wedge

with uniform impedance surface. The diffraction by a rightangle

wedge with different impedance boundary conditions at

its two surfaces is first considered. A functional transformation

is used to simplify the boundary conditions. The eigenfunction

solutions for the transformed functions are replaced by integral

representations, which are then evaluated asymptotically by the

modified Pauli–Clemmow method of steepest descent. The asymptotic

solution is interpreted ray optically to obtain the diffraction

coefficient for the uniform geometrical theory of diffraction

(UTD). The obtained diffraction coefficients are related directly to

Keller diffraction coefficients in uniform version. The total field

is continuous across the shadow of the geometrical optics fields.