Performance-defining parameters of radio-navigational aids

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In its broadest aspect, the object of the paper is to draw attention to the need for a formal theory of radiolocation. An approximate analogy is drawn between the time, about 20 years ago, when the ‘knowhow’ of the experienced communication engineer was being translated into a formal theory of communication, and the present time, when, despite the existence of a corresponding expertise in the field of radiolocation, no serious attempt has been made to define a formal theory.In radiolocation, the concept of trading ‘aperture’ or ‘baseline’ for accuracy, very closely allied to the concept of trading frequency bandwidth for suppression of noise in communication systems, is very well known, and has probably been fully exploited, but theoretical limits have not yet been defined.The further concept that the frequency bandwidth of a radiolocation signal can also be traded for error suppression, though not new, has probably not been fully explored, and certainly not fully exploited. It is therefore a major object of the present paper to draw attention to this important aspect.A complete assessment of the value of an increased frequency bandwidth is not attempted, and no attempt is made to define an ideal system. However, by analysing a comparatively simple and practicable system which employs wide-deviation frequency modulation, and lends itself to a simple mathematical treatment, it is shown that a great improvement is possible.A simple aircraft approach-path guidance system comprising two laterally spaced, synchronously frequency-modulated transmissions is shown to have a greatly improved error-suppression characteristic, compared with conventional systems.The concept of ‘effective bandwidth’, as already used in communication theory, is introduced, showing that, though the frequency bandwidth used by a single location device may be very large, this may not be prohibitive, as a number of devices may share the same frequency band without mutual interference. This leads to a suggestion for a new aircraft guidance system providing azimuth indication, as in VOR, approach-path guidance, distance-to-fly indication, glide path and distance along runway, all on a single radio-frequency channel.