"vector cross-product direction-finding" with an electromagnetic vector-sensor of six orthogonally oriented but spatially noncollocating dipoles/loops

Direction-finding capability has recently been advanced by synergies between the customary approach of inter ferometry and the new approach of 'vector cross product' based Poynting-vector estimator. The latter approach measures the incident electromagnetic wavefield for each of its six electromagnetic components, all at one point in space, to allow a vector cross-product between the measured electric-field vector and the measured magnetic-field vector. This would lead to the estimation of each incident source's Poynting-vector, which (after proper norm-normalization) would then reveal the corresponding Cartesian direction-cosines, and thus the azimuth-elevation arrival angles. Such a 'vector cross product' algorithm has been predicated on the measurement of all six electromagnetic components at one same spatial location. This physically requires an electromagnetic vector-sensor, i.e., three identical but orthogonally oriented electrically short dipoles, plus three identical but orthogonally oriented magnetically small loops-all spatially collocated in a point-like geometry. Such a complicated 'vector-antenna' would require exceptionally effective electromagnetic isolation among its six component-antennas. To minimize mutual coupling across these collocated antennas, considerable antennas-complexity and hardware cost could be required. Instead, this paper shows how to apply the 'vector cross-product' direction-of-arrival estimator, even if the three dipoles and the three loops are located separately (instead of collocating in a point-like geometry). This new scheme has great practical value, in reducing mutual coupling, in simplifying the antennas hardware, and in sparsely extending the spatial aperture to refine the direction-finding accuracy by orders of magnitude.