Radiogoniometers for high- and very-high-frequency direction-finding

The paper is concerned with the design and performance of inductive radiogoniometers for use in d.f. systems operating in the frequency band 3?100 Mc/s. The general principles of design are discussed, and it is shown that the main considerations are the coupling law, the electrical symmetry of the field coils and the coupling factor. The principal component of the instrumental error is the coupling error, and two methods of reducing it are described. One involves the use of a distributed search-coil winding, and the other the use of a compound-wound type of search coil. It is shown that, if the turns of the search-coil winding are wound on a cylindrical former so that they cover the surface completely, the coupling error is negligible, irrespective of the form of the field coils. Four h.f. instruments designed on this principle are described, and details of their performance are given. In the compound-wound search coil the winding is in two sections, the planes of which are set at an angle to each other. It is shown that the coupling error is dependent upon this angular separation and upon the configuration of the magnetic field. An investigation into the design of the field coils indicates how the most suitable field configurations may be obtained. The design and construction of a v.h.f. goniometer embodying these principles is described, and its measured performance provides confirmation of the theory of operation. The importance of electrical symmetry of the field coils is pointed out, and the ways in which it is affected by the design of the goniometer are discussed. Comparison between goniometers of the two types shows that, in general, for medium and high frequencies the distributed search-coil winding is the more suitable, and for v.h.f. operation that with the compound-wound search coil. In an appendix the operation of the inductive goniometer as a phase shifter is considered theoretically, and it is shown that it has the same instrumental error when used in- this manner as when used as an amplitude comparator in a direction-finder.