A Ray-Tracing Technique for Determining Ray Tubes in Anisotropic Media

Ray-tracing techniques are commonly used for calculating the paths taken by electromagnetic waves in a medium that has an associated refractive index, such as the earth's ionospheric plasma. Ray equations derived from Hamilton's equation are usually used to determine ray paths and ray tubes defined by tracing adjacent rays separately. There are advantages in describing ray tubes in terms of a main ray and variational rays. In this paper, equations for variational rays are derived for anisotropic inhomogeneous media such as the earth's ionosphere. The ray-tracing technique is ideal for simulating ionospheric propagation experiments, and examples are given of ground illumination as a function of ground range and frequency.

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