FRESNEL DIFFRACTION OF RF WAVEFRONTS

摘要

The objective of this program was to develop the necessary mathematics including a computer program to predict and define the RF and geometric shadow of any proposed (or existing) obstruction in the coverage volume of airspace of radar facilities operating in appropriate aeronautical service bands. The RF shadow calculation includes the effects of Fresnel diffraction by a perfectly-conducting rectangular obstruction through the use of Geometric Diffraction Theory. Both the line-of-sight (geometrical-optic) shadow and Fresnel diffraction effects are calculated by the computer program for arbitrary incidence and observation angles relative to the obstacle. Signal degradation relative to the obstacle-free field, and for desired combinations of transmit and receive polarizations, was described by providing plots of arbitrarily chosen dB levels at chosen observation planes behind the obstruction. Circularly cylindrical, spherical, and convex polyhedron obstructions were also considered but only to determine geometric shadowing. A flight test program was conducted to experimentally validate the computer program using a rectangular obstruction at three different viewing angles. The experimental results were in good agreement with predicted values. (Author)