Medium frequency body loop antenna for use underground

Radio communication underground in mines is possible by a variety of propagation mechanisms. Where there is a need for the communication system to be independent of special-purpose cables, such as `leaky feeders´, then maximum propagation range is only possible if low-frequency radio systems are used. The usual requirement that the equipment be portable imposes severe restrictions on the antenna. The author reviews this problem briefly and describes a loop antenna, developed specifically for this application, which is worn by the operator. The magnetic dipole or small loop has particular advantages over the more conventional short electric antenna when both are surrounded by a lossy dielectric medium. The need to achieve maximum magnetic moment is discussed as is its relationship to the loop geometry and the required operating bandwidth. The effect of the operator´s body on the antenna´s characteristics is also discussed