Accurate ILS and MLS performance evaluation in presence of site errors

A powerful and versatile analytical approach is outlined for performing the site evaluation of instrument landing systems (ILS) and microwave landing systems (MLS) without resorting to the current experimental methods. The problem is treated as one of scattering, using a ray-theoretic approach. A multiwedge model of the terrain ahead of the antenna assembly is generated from standard survey data and an exact ray-tracing procedure is evolved to trace all the rays between the antenna elements and approaching aircraft. The power of the current uniform diffraction theory (UTD) to evaluate scattered fields from wedges is extended to include the impedance and roughness of the wedge, and the theory is applied to the multiwedge terrain model for evaluating the field. The results are reduced to a form compatible with ICAO (International Civil Aviation Organization) specified tests and compared with experimental data from real airports