Redundancy in the measurement of HF direction finding

Abstract

Radio direction finding, especially in single site location, techniques must resort to high resolution algorithms using decorrelation factors for the impinging modes, such as Doppler frequency shift or group delay. We have proposed to use polarization, which is a function of the type of mode (O, X) and of direction of arrival (DOA), as another factor of separation. We use space and polarization diversity and we apply them to high resolution algorithms. A first technique is developed from a nonlinear frequency analysis associated with an interferometry method. It deals with narrow band signals were Doppler and polarization are separation factors. A second method uses the MUSIC algorithm in an original way, taking into account the knowledge of each sensor's response. This technique processes narrow band or wide band signals, a wide bandwidth implies a group delay difference separation factor. The paper also present some results of direction of arrival measurements obtained from European broadcast transmitters, and compares the estimations related to each technique. First, the experimental system is described, and each direction finding method is presented. Finally, experimental results obtained on a square array are given. Redundant measurements and the methods used to estimate the DOA are discussed.