Air Force

Compact, high-efficiency, ELF/VLF antenna

For use in long wavelength communications and as a radiation shield for satellite-based electronics

Communications

Due to the difficulty of fabricating antennas configured to radiate the long waves of the VLF and ELF bands, such antennas have been used in few applications. Since these bands are capable of modulating some extremely low bitrate data, they have found some usefulness in penetrating sea water and rock, and thus enable subterranean or sub oceanic radio communications, but those are limited applications. Compounding their lack of usefulness, conventional means of transmitting in these bands necessitate the use of long power lines, or earthed dipoles, as leads. These leads could be on the order of several kilometers long. Due to the inefficiency of this method, considerable amounts of electrical power are required to energize the antenna.

Air Force researchers have developed a new antenna which dramatically improves on the radiation efficiency of VLF and ELF antennas – with a very small footprint. As a result of the improved efficiency, the device solves many problems encountered by satellite-based conventional loop and dipole antennas used for excitation of electromagnetic VLF and ELF waves in the ionosphere. The novel approach utilizes two concentric loop antennas transmitting at slightly different frequencies. Each loop antenna excites the predominantly electrostatic component of the VLF wave spectrum in the form of lower oblique resonance (LOR) oscillations. Nonlinear interaction of LOR waves creates a region around the loop antennas that yields performance tantamount to a much larger antenna, simultaneously re-radiating the VLF and ELF wave energy with an order of magnitude greater radiation efficiency.

Applications are both terrestrial and space-based. It may find utility in military and commercial spacecraft for removal or deflection of highly energetic particles in the ionosphere that are harmful to satellite electronics (radiation hardening), VLF and ELF communications, locating and probing underground structures, and subterranean pipeline inspection.

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