Terrain modelling of glideslope for instrument landing system

The paper makes a contribution to the evaluation of irregularities introduced in electronically defined glideslopes of UHF instrument landing systems (ILS) by the unevenness of the terrain around the glideslope antenna. Various methods of physical and geometric optics have been applied in recent years to model and estimate the glideslope aberration at given locations prior to actual installation. A systematic study of various methods is made in the paper. A general treatment is evolved, which is capable of exhaustively handling arbitrary ray order effects and topography. The uniform asymptotic theory has been applied to the ILS problem and results compared with the uniform theory of diffraction. The results of actual case studies are presented.