Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere

Details Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere

Jun 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008georl..3512101c&link_type=abstract

Geophysical Research Letters, Volume 35, Issue 12, CiteID L12101

Physics

8

Ionosphere: Auroral Ionosphere (2704), Ionosphere: Instruments And Techniques, Radio Science: Waves In Plasma (7867), Radio Science: Ionospheric Physics (1240, 2400), Radio Science: Nonlinear Phenomena (4400, 7839)

Scientific paper

ELF/VLF radio waves (300 Hz-30 kHz) are difficult to generate with practical antennae, because of their extraordinarily long (10-1000 km) wavelengths, and the lossy nature of the Earth's surface at these frequencies. ELF/VLF waves have been successfully generated via amplitude modulated (AM) HF (2-10 MHz) heating of the lower ionosphere. Through the temperature-dependent conductivity of the lower ionospheric plasma, a patch of the ionospheric current becomes a large radiating `antenna'. We implement a new method of ELF/VLF wave generation, herein named `geometric modulation', involving scanning the HF heating beam in a geometric pattern without modulating its power. Utilizing results from the upgraded 3.6 MW radiated HAARP HF antenna array, we show that geometric modulation can enhance ELF/VLF wave generation by up to ~11 dB over the conventional AM method. Geometric modulation also allows directional launching of the signal into the Earth-ionosphere waveguide, forming an unprecedented steerable large-element ELF/VLF ionospheric phased array.

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