Signal processing in DF has, until recently, been almost entirely of an analogue nature. The spinning goniometer usually used in a Wullenweber system is an example: the inputs to the goniometer are the signals from a selected arc of elements and the output is fed through a single-channel receiver which determines the narrow frequency band to be examined. The development of multichannel HF receivers in recent years has opened up the possibility of using instead some form of digital processing; the amplitudes and phases of the element signals at a selected frequency can be measured, recorded digitally and processed in a computer program. The experimental and mathematical techniques are referred to collectively as wavefront analysis (WFA). The aim is to resolve the wave-field into its component rays and to print out the ray parameters. Direct analytic or iterative attacks on the equations relating the ray parameters to the measured signals become very unattractive when more than a small number of rays are present. However, a general method of solution, applicable to almost any form of antenna array, can be used with fading signals (Gething, 1971). In this chapter some simple examples of the technique will be given for idealised problems involving neither noise nor measurement errors, in order to explain the principles involved.

Inspec keywords: radiowave propagation; signal processing; goniometers; wireless channels; radio receivers; antenna arrays; radio direction-finding

Other keywords: Wullenweber system; ray parameter; wave-field; single-channel receiver; multichannel HF receiver; direction finding; signal measurement; signal processing; antenna array; direct analytic attack; spinning goniometer; narrow frequency band; wavefront analysis; fading signal; digital processing; iterative attack

Subjects: Radionavigation and direction finding