VLF mode analysis using a ceramic dielectric model of the Earth-ionosphere waveguide

The mode content of very-low-frequency (VLF) energy propagating away from a horizontally polarized source over long ice-covered paths is studied by means of a laboratory model of the earth-ionosphere waveguide that incorporates one lossy wall. A reflecting upper boundary simulates the nighttime ionosphere; powdered ceramic materials are used at 4 GHz to represent the 15 kHz properties of air and Antarctic ice. The model is a flexible experimental tool potentially applicable to a number of propagation problems. In terms of the immediate study, namely, VLF propagation on the Antarctic continent, it is demonstrated that the three lowest TE modes are sufficient to represent the total far field under the assumed conditions. The laboratory results agree well with theoretical predictions; their relationship to ray concepts is pointed out.