A comparison of MUSIC and an iterative null steering technique for the resolution of multi-moded ionospherically propagated HF radio signals

Assuming that ionospherically propagated radio signals are comprised of a number of discrete modes each having a planar wavefront, measurements of the amplitudes and phases observed on an array of spaced antennas can yield the direction of arrival (DOA) of a signal in both azimuth and elevation. Work has previously been reported by Warrington and Jones (1991) in which the DOA of signals radiated from a number of European broadcast transmitters in the frequency range 9-15 MHz were determined by means of interferometric techniques. Some of the measurements employed for that study have been reprocessed with two super-resolution direction finding algorithms: (a) the MUSIC algorithm proposed by Schmidt (1986) and (b) an iterative null steering technique based on the IMP algorithm developed by Clarke et al. at DRA, Malvern and the DOSE algorithm developed by Zatman and Strangeways (see IEE International Conference on Antennas and Propagation, IEE Conference Publication 370, p.415-418, 1993) at the University of Leeds.