A technique for modeling plane wave propagation through inhomogeneous media and plasma layers with different electron densities is presented. The technique is based on transmission line theory. Therefore, a general technique is introduced for solving complex transmission line systems. A data structure and algorithm for representing, and simultaneously solving for all nodes within the transmission line network is presented. The method is based on representing the network as a recursive tree structure and solving for the voltage, current, and impedance at each node using recursive programming techniques. First, all frequency dependent parameters within the tree structure are updated, then in a post-order traversing of the tree, the impedance at each node are computed followed by a pre-order traversing of the tree to compute node voltagesand currents. For plane wave propagation, the reflection coefficient, the electric field andmagnetic field are computed. The method is applied to normal incidence but can easily be extended to oblique incidence. A tapered transmission line model was used to verify the algorithm. In addition, an example was provided verifying the ability to compute the frequency response and impulse response of a system with a plasma. Finally, the application of the technique to model the heat tile and the plasma that develops on either aero-assist or spacecraft re-entry is presented.This paper is based on work done at the Center for Communication and Signal Processing (CCSP) at North Carolina State University by the author in 1987. In addition, the paper presents work which was supported by NASA Langley Research Center under Contract NASI-1x925. The author was the Principal Investigator.