Leaky waves supported by uniaxial plasma layers

Each discrete complex wave supported by a uniaxial layer corresponds to an isolated singularity in an appropriate Green´s function. The location of a singularity depends on the geometry, plasma density, and the direction of the magnetic field, but not on the source. We have derived the discrete solutions for an infinite magnetic field that is parallel or perpendicular to the slab interfaces. For a parallel field, analytic expressions are obtained that yield the exact locations of the complex pole Ioci. Although similar expressions cannot be obtained if the field is perpendicular, the resonance relation which locates the poles can be solved by methods developed for an isotropic plasma. We find that improper modes and surface waves can be supported in the case of a parallel field, while a perpendicular field permits spectral complex modes as well. These results are applied to a Kirchhoff-Huygens integration of the leaky-wave distribution excited by a magnetic line source or an annular slot. A close correlation is shown between the radiation pattern derived by this procedure and the exact pattern calculated by the method of steepest descent. In particular, it is shown that the appearance of a peak in the pattern can be analytically correlated with the contributing pole, provided it corresponds to a dominant leaky wave.