Refraction Anomalies in Airborne Propagation

Propagation at 250-10,000 mc often encounters: 1) dense fadings where the radio signal fluctuates spatially with large amplitudes and small spacings from maxima to minima, e.g. amplitudes of up to 40 db and spacings at 3000 mc of 1 mile; 2) radio holes, where the signal falls spatially to a level often 15 db or more below the levels outside; 3) antiholes, where the signal fluctuates spatially with large amplitudes and irregular spacings; 4) radio ducting, including cases where the transmitter or receiver is far above a ducting layer in the air. The anomalies (1-4) are portrayed by ray tracings using a differential analyzer which solves the simplified ray equation d2h an(h, x) I dx2 ah a Both hypothetical-prototype and complex-measured refractive index profiles of the atmosphere are used for the analog computation of the ray tracings which are interpreted to explain refraction anomalies in radio-wave propagation and are compared with signal-strength measurements. They involve divergence of rays, and concentration and crossing of direct rays in multipath transmission. Resulting radar angular and range errors are shown where the radar sights a target at a) multiple elevation angles, of under 1 degree, which deviate by up to few tenths of a degree from the angle obtained if the atmosphere were standard, and b) multiple range corrections, for a 200-mile range, which deviate by few tens of feet from the standard correction.