Propagation in a rectangular tunnel with two lossy walls

We re-examine one model in the classic paper by Mahmoud and Wait (for original paper see Rad. Sci., vol. 9, p. 1147-1158 (1974)) on rectangular tunnels. The model consists of two perfectly conducting and two imperfectly conducting walls. We have verified and reproduced the results in Mahmoud and Wait for both their modal and ray-optic solutions. The x-component of the electric field obtained in Mahmoud and Wait exhibits identical fall-off characteristic over axial distance. However, because we are interested in local placement of sensors, we have used a much finer digitization. We note that local field variation is as high as 30 dB, a fact that would greatly influence the signal-to-noise ratio in a receiver as it is moved down the tunnel. This rapid variation has been obtained by other researchers for other geometries.