Accession Number:

ADA220969

Title:

Understanding Tropscatter Propagation

Descriptive Note:

Master's thesis

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH

Personal Author(s):

Report Date:

1990-03-14

Pagination or Media Count:

252.0

Abstract:

Although troposcatter communications systems have shortcomings, this transmission scheme has found consistent use in several applications. This thesis discusses troposcatter propagation with emphasis on theory, characteristics, and prediction tools. Theoretical understanding of the troposcatter propagation mechanism is rooted in atmospheric phenomena, specifically--refractivity and turbulence. Two modes of transmission exist incoherent scatter, if refractivity irregularities exist as turbulent blobs, and quasi-coherent scatter, if irregularities arrange themselves in layers. Frequency and meteorological parameters define the dominant mechanism. One can expect received signal levels to exhibit distance and frequency dependence short and long-term fading aperture-to-medium coupling loss and diurnal, seasonal, climatic, and meteorological variations. Diversity techniques are indispensable in thwarting short-term fading. Atmospheric multipath is known to limit analog system bandwidths yet digital systems are prone to the related delay spread phenomenon which causes intersymbol interference. Adaptive processing is used to overcome this problem and can further improve digital performance through implicit diversity. Most troposcatter prediction methods are rooted in empirical expressions. Unfortunately, all the methods suffer shortcomings with reliance on surface refractivity and incorrect coupling loss calculations topping the list. Accuracy can improve if tools such as the Parl or Radiometeorological methods effectively model gradient activity within the common volume. Theses.

Subject Categories:

  • Atmospheric Physics
  • Radiofrequency Wave Propagation
  • Radio Communications

Distribution Statement:

APPROVED FOR PUBLIC RELEASE