Secondary surveillance radar monopulse target azimuth error estimation due to obstacle shadowing

Recorded data from some secondary surveillance radar (SSR) stations has shown deviations positional accuracy when the SSR antenna shadowed by neighbouring man-made structures (such as communication masts, buildings and radomes). Modern SSR monopulse receivers estimate the azimuth of aircraft through the orientation of the incident planar wavefront. Obstacles in the propagation path diffract part of the electromagnetic wave energy and as a result, the electric field across the antenna array is subject to a disturbance. The resultant azimuth error in the shadowed sector depends on the width and height of the obstacle and on its position relative both to the radar and the aircraft. A method to estimate the azimuth error curve due to obstacle shadowing based on cylindrical diffraction theory is described. A comparison between measured data and the estimated error curves reveals that azimuth errors can be very precisely calculated. Accurate estimation of azimuth errors due to obstructions has increasing significance for operators of SSRs. Radar performance must continue to be safeguarded in the face of increasing pressure to allow development on or near radar sites. Methods of estimating the effects of such developments will play a key role in future safeguarding.