Multiple-tuned VLF antennas

Different approaches to feeding two multiple-tuned VLF antennas with regard to antenna performance and tuning are compared. Both antennas may be fed separately, or only one may be fed and the other grounded through a previously tuned coil. The antennas may either be connected or separated at their capacitive ends. The maximum bandwidth-efficiency product of all these arrangements is the same. Connected antenna systems achieve this maximum for all adjustments with in-phase base currents, and the most favorable tuning depends on the efficiency desired. If only one antenna is fed, the tuning procedure is quite simple, because only current magnitudes have to be adjusted. Retuning of the coils in the nonfed upleads is not necessary if changes are small compared with the magnitude of the antennas´ coupling reactances. Connected element systems are particularly stable. These properties can be transferred to other multiple-tuned antenna systems of electrically short elements with top capacitances