Abstract: Radio direction finders using the principle of periodic scanning of a circular array inherently display a bearing error related to the group delay through the receiving, detection and evaluation process. Correcting by subtracting a constant .theta..sub.o is simple but it is difficult to keep .theta..sub.o constant. The present invention cancels the group delay error instead of compensating for it with a predetermined constant. Scanning is done at angular velocities .OMEGA..sub.1 and .OMEGA..sub.2 for m turns and n turns respectively. The parameters are related by the formulae.omega..sub.2 /.omega..sub.1 =m/n (1)n-m=1 (2)Group delay errors are cancelled by computing the true bearing from the formulan.theta..sub.2 -m.theta..sub.1 =.theta.where .theta..sub.1 and .theta..sub.2 are the bearing readings at .omega..sub.1 and .omega..sub.2 respectively and .theta. is the true bearing of the radio target.

Abstract: A novel Direction Finding system is described, using a small aperture circular array of vertical dipoles, the outputs of which are rotated in phase by angles corresponding to their angular location on the array circle. A phased ring combiner is used to add the dipole pair outputs, giving two resultant waveforms, one advanced in phase and the other retarded by the same angle .theta., where .theta. is the relative bearing angle of the incoming signal. The phasing elements are made independent of the signal frequency either by the use of all-pass networks or by prior conversion to a fixed intermediate frequency. DF processing can be performed by a digital meter which computes the phase difference between the two resultant waveforms. In addition, an orthogonal DF display is available through a .SIGMA./.DELTA. conversion.