Ray-density normalization for ray-optical wave propagation modeling in arbitrarily shaped tunnels

This work is concerned with the calculation of natural electromagnetic (EM) wave propagation and the determination of the propagation channel characte ristics in highway or railway tunnels in the ultrahigh-frequency (UHF) rang e and above (>300 MHz). A novel ray-tracing technique based on geometrical optics (GO) is presented. Contrary to classical ray tracing, where the one ray representing a locally plane wave front is searched, the new method req uires multiple representatives of each physical EM wave at a time. The cont ribution of each ray to the total field at the receiver is determined by th e proposed ray-density normalization (RDN). This technique has the further advantage of overcoming one of the major disadvantages of GO, the failure a t caustics. In contrast to existing techniques, the new approach does not u se ray tubes or adaptive reception spheres. Consequently, it does not suffe r their restrictions to planar geometries. Therefore, it allows to predict the propagation of high-frequency EM waves in confined spaces with curved b oundaries, like tunnels, with an adequate precision. The approach is verifi ed theoretically with canonical examples and by various measurements at 120 GHz in scaled tunnel models.