The novelty of the 3D beamspace domain, maximum likelihood (3D BDML) bearing estimation scheme is its judicious exploitation of the fact that the respective beams associated with any three classical beam-forming vectors which are mutually orthogonal have M-3 nulls in common, where M is the number of elements comprising a uniformly spaced, linear array. Exploitation of this property yields an estimation scheme that is nearly as computationally simplistic as the 2D beamspace bearing estimation technique based on sum and difference beams employed in conventional monopulse radar. To provide robustness to the severe signal cancellation occurring across the array when the direct and specular path signals arrive 180 degrees out of phase at the aperture center with roughly equal amplitude, frequency diversity is incorporated into 3D BDML. The coherent signal subspace concept of H. Wang and M. Kaveh (1985) is invoked as a means of retaining the computational simplicity of single-frequency 3D BDML.
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