Accession Number : ADA063873

Title :   On High-Frequency Ionospheric Ducting - A Review

Corporate Author : ROME AIR DEVELOPMENT CENTER GRIFFISS AFB NY

Personal Author(s) : Toman, Kurt

PDF Url : ADA063873

Report Date : Sep 1978

Pagination or Media Count : 20

Abstract : The observational evidence for long-range propagation of high- frequency radio signals began to accumulate in 1926 when transatlantic communication links had been established. In 1927, signals were detected that had propagated over large distances or circled the earth with little attenuation. LONG-RANGE AND ROUND-THE-WORLD (RTW) signals showed preferred periods of occurrence. Relatively high angles of incidence (20 deg relative to the horizontal) of such signals at the receiver, paired with low attenuation, ruled out conventional multihop propagation. An ionospheric refractive index boundary was postulated along which the signal propagates in a glancing- incidence low-loss mode. The transmission path of observed long-delayed signals, originating from artificial earth satellites, was found to be located in the twilight zone. Experiments using ground-based transmissions confirmed the role of ionospheric absorption and tilts for the occurrence of long-range and RTW signals. Detailed explanations for ionospheric ducting were provided using several theoretical concepts and analyses. The (mu)(r) (refractive index times geocentric distance) - diagram was used for the study of ray propagation in a spherically stratified multi-layered model ionosphere depicting characteristics of the ground-detached glancing-incidence mode. Numerical ray-tracing computations were made using model ionospheres with horizontal gradients.

Descriptors :   *IONOSPHERIC PROPAGATION, ELECTROMAGNETIC SCATTERING, HIGH FREQUENCY, INTERNAL REFLECTION, LAYERS, LONG RANGE(DISTANCE), LOW LOSS, RAY TRACING, REFRACTIVE INDEX, TRANSMISSION LOSS

Subject Categories : Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE