Superdirective antenna arrays for improved VLF reception

Superdirective antenna arrays offer a practical and significant improvement in the reception of VLF radio signals. Based on supergain techniques, such arrays enhance the SNR by the use of a highly directional pattern without occupying more than a few per cent of the space that would be required for a conventional array, and do not degrade the bandwidth. Supergain techniques are not usually of practical interest because of unavoidable losses in efficiency and in many cases, drastic reduction in bandwidth resulting from interaction between elements. It is shown that most of the problems with superdirectivity are peculiar to the case of efficient antennas, and do not apply to VLF receiving antennas in which extremely low efficiencies are easily tolerated.