Abstract :
The computer program under discussion is ALDAS which computes the radiation pattern of a low gain antenna when a conducting structure is nearby. The geometry of the structure is modelled by the use of simple shapes, flat plates and cylinders of circular cross-section with the addition of more complex shapes such as general ellipsoids for the fuselage or the main structural element. Reflections from each element of the structure are found using geometrical optics techniques. The diffracted rays are of two types, an edge diffraction where a ray striking an edge is diffracted into a cone of rays, and curved surfaces where a ray travels along a geodesic of the surface shedding rays tangentially. The procedure is a mixture of geometry (the rays must be traced) and electromagnetic theory (when the correct ray is found, GTD/UTD must be employed to find the field along the ray)
