C.W. radio aids to approach and landing

Abstract

The problems involved in the design of landing approach systems are complicated by psychological and aerodynamic considerations. The display of intelligence from the system is of great importance, and the form that it should take has influenced system design.The first attempt to provide guidance in azimuth made use of the magnetic field surrounding a cable on the ground, but this was superseded by radio systems. Keyed signals produced by overlapping field patterns were favoured in this country until fairly recently, but these have been replaced by modulation separation systems as being more suitable for operation of the preferred indicator.Guidance in elevation is provided by a “glide-path” system, which is preferably of the overlapping pattern type and provides a straight line of descent.Distortion of the course characteristics by re-radiation from objects near the transmitter is a problem which can only be solved by restricting the energy radiated towards the interfering object. This is achieved in present systems by the use of arrays, but the employment of equipment operating on centimetre wavelengths offers convenience in obtaining greater directivity.It is considered desirable to control the automatic pilot from the landing approach system, and experiments to this end are in progress, the results of which will probably affect the design of landing systems.