Characteristic properties of underground radio communications

The problem of underground radio communication is considered. Its necessity and difficulties of its realization are shown. The main difficulty is quick attenuation of transmitted signal. A version of the communication system, based on a compromise between the large dimensions of the antenna and the great earth losses, is suggested. In authors' opinion, the operation frequency must be medium frequency. Antennas with sinusoidal and cosine distribution of current are compared. It is offered to use a directional antenna structure, consisting of flat self-complementary antennas of a new type.