Measurements of direction of arrival of HF sky wave signals by means of a wide aperture antenna array and two super resolution direction finding algorithms

From measurements of the amplitude and phase of ionospherically propagated HF radio signals received at several spaced antennas, the direction of arrival of the signals in both azimuth and elevation can be determined. A series of measurements has been undertaken using a wide aperture antenna array on signals received from several European broadcast stations (in the 9-15 MHz range) at distances of up to about 1400 km, and the directions of arrival estimated by means of two super-resolution algorithms; MUSIC and an iterative null steering method (an approximate maximum likelihood estimator) based on the IMP and DOSE algorithms. A detailed comparison of the performance of the two algorithms has been undertaken, and it is concluded that the null steering algorithm is significantly better than MUSIC at resolving the various propagation modes, particularly for short signal analysis periods