Radiation of very low and extremely low frequencies (VLF & ELF) by a natural antenna based on an island or a peninsula structure

The idea of using a geophysical structure, such as an island or a peninsula, to radiate extremely low frequencies (ELF) or very low frequencies (VLF) was proposed approximately 40 years ago. It seems that all efforts to implement this idea remained in a premature experimental phase, while it is known that an ELF system operating at 75 Hz was developed by the United States Navy twenty years ago. In the present paper, a historical review is presented of the previous work on this topic. In order to examine the possibility of constructing such a “natural antenna,” the authors developed an experimental system and carried out measurements at the Kynosoura peninsula near Marathon-Greece. They constructed an experimental ELF-VLF antenna in the frequency band of 1–12 kHz. Both the input impedance and electromagnetic field quantities were measured during August-October, 2000, and these are presented. A comparison of the measured results with theory shows that an island or a peninsula can't operate as a slot radiator. However, efficient operation can be achieved using a vertical-loop mode, utilizing an island in which the current return path is achieved through underground media or by a linear wire antenna lying on the island.