An improved computer model for ILS glideslope evaluation

Instrument landing system (ILS) is a very important navigational aid at most major airports of the world. However, their performance is directly affected by the features of the site in which they are located. Since the on-site validation of the ILS performance is normally done through costly and time consuming experimental methods, considerable efforts have been made in the past to develop analytical approaches as an alternative to the experimental methods. This paper though follows the earlier approaches of multi-plate terrain modeling, presents a very powerful and exhaustive ray tracing technique and a modified formulation for determining the electromagnetic fields. Innovative techniques are introduced at each stage to make the model versatile enough to handle the effects of the undulation, the roughness and the impedance of the terrain and also to reduce computational requirements to a minimum. The results obtained from the method developed here are compared with the earlier methods and the actual measurements and good agreement is shown.