Influence of ground reflections on radar target-tracking accuracy

The radar target-tracking error introduced by ground reflection of the radar `echo¿ has been calculated for a conventional static-beam split autotracking radar. The results and the analysis in the paper apply to a uniformly illuminated parabolic reflector which gave a beamwidth of 1° at a wavelength of 3cm. It is shown that the classical propagation theory adequately explains the ground reflection errors. Both theory and experiment show that there will be tracking errors of ±10¿ at target elevations approaching 0° for ground reflectivities of about ¿0.4. At target elevations of 5° the tracking error can be ±1¿, which, even at this large elevation angle, would be the most important factor governing the target-tracking performance of present-day precision radars. A simple formula for calculating the peak tracking error is shown to be accurate down to elevation angles of 0.5°. Antiground-reflection screens placed at the reflection point give substantial improvements in tracking. The screens have to be sufficiently wide to prevent any appreciable amount of radiation from the image of the target diffracting round the vertical edges of the screen for all the possible target azimuth angles. In many cases, therefore, screens would not be practicable.