Microwave propagation of surface waves

Experimental results of field amplitude and delay-time variation in microwave propagation in the presence of lossy media (dielectric or conductor) are reported. When the surface of the medium is situated very close to the wave paths, we observe, on the average, a slight superluminal behavior in the presence of a dielectric board, while an opposite subluminal behavior is evidenced when a metal plate is placed over the board. These features are qualitatively confirmed by measurements on the nature of the propagation-admittance. The results are interpreted on the basis of a simple electromagnetic model.