“Vector Cross-Product Direction-Finding” With an Electromagnetic Vector-Sensor of Six Orthogonally Oriented But Spatially Noncollocating Dipoles/Loops

TLDR

Vector cross‑product direction‑finding relies on measuring all six electromagnetic field components at a single point, requiring a collocated dipole‑loop array that suffers from severe mutual coupling and high hardware complexity. This study demonstrates that the vector cross‑product estimator can be applied even when the dipoles and loops are spatially separated. By deploying the three orthogonal dipoles and three orthogonal loops at distinct locations, the authors reduce mutual coupling and sparsely extend the aperture to preserve the cross‑product calculation. The resulting scheme markedly simplifies the antenna hardware, lowers coupling, and improves direction‑finding accuracy by orders of magnitude.

Abstract

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.