Accuracy of Adcock Watson-Watt DF in the Presence of Channel Errors

Adcock Watson-Watt (AWW) methods for radio direction finding (DF) have a long history, but are often still used in modern, wideband DF systems. A number of sources of error can reduce the accuracy of the DF estimates produced. One such source of error is due to unaccounted for amplitude and phase errors in the three receiver channels; perhaps due to unbalance in the analogue circuitry, or component tolerance in the receive filters. This paper provides a theoretical analysis of the impact of complex gain errors on the expected DF estimates. When combined with the effects of receiver noise, analytical performance curves for the AWW system can be produced. For small array apertures, it is shown that AWW can actually outperform more sophisticated N-channel DF such as correlative interferometer, maximum likelihood and subspace techniques.