Fresnel Zone Theory of VLF Coupling into the Earth-Ionosphere Waveguide.

• Main Author: Bradford, W. R.
• Other Authors: NAVAL ELECTRONICS LAB CENTER SAN DIEGO CA
• Format: Text
• Language: English
• Published: 1971
• Subjects: Cybernetics; Radiofrequency Wave Propagation; Radio Communications; (*RADIO TRANSMISSION; THEORY); (*RADIO RECEPTION; VERY LOW FREQUENCY); (*INFORMATION THEORY; PROPAGATION); RADIO TRANSMITTERS; RADIO RECEIVERS; WAVEGUIDES; IONOSPHERE; EARTH(PLANET); DIURNAL VARIATIONS; INTERFACES; REFLECTIVITY; GREENLAND; NORWAY; EIGENANGLES; FRESNEL ZONES; RAY TRACING; Greenland; Norway; Thule
• Online Access: http://www.dtic.mil/docs/citations/AD0892152; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD0892152

VLF propagation over long paths does not fill the entire great circle arc between transmitter and receiver at the ionospheric altitude. It is blind to the appearance of the terminator over either station. This report concerns one method of calculating the spacial extent of these 'excitation' regions. A ray is drawn from the transmitting station so its angle of incidence at the ionosphere is the real part of the eigenangle. Other rays in the plane of incidence intersect the ionosphere in a great circle arc. The Fresnel zone phase coherence criterion, + or - one quarterwave, is applied to limit the extent of this arc. The arithmetic mean of central angles from the transmitter to each end of the arc is a measure of the excitation region. Calculations are carried out for 12 eigenangles. These represent day and night profiles at three latitudes over water. The Thule-Norway path is also represented.