Diversely polarized antenna-array signal processing

Abstract

The dissertation is composed of three distinct but related components, which relate to direction finding and/or polarization estimation with diversely polarized antenna arrays. The three parts are briefly summarized below: (1) "Vector cross-product direction-finding" with an electromagnetic vector-sensor of six orthogonally oriented but spatially non-collocating dipoles / loops. Direction-finding capability has recently been advanced by synergies between the customary approach of interferometry 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 electro-magnetic isolation among its six component-antennas. To minimize mutual coupling across these collocated antennas, considerable antennas-complexity and hardware cost could be required. Instead, Chapter 2 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 extending the spatial aperture to refine the direction-finding accuracy by orders of magnitude. (2) Various triad-compositions of collocated dipoles/loops, for direction finding & polarization estimation. To form a collocated triad of orthogonally oriented dipole(s) and/or loop(s), 20 different compositions are possible and these compositions are investigated in Chapter 3. For each such composition: (i) closed-form formulas are produced here to estimate the azimuth-elevation direction-of-arrival and the polarization-parameters, or (ii) reasoning is given why such estimation is inviable. (3) Polarization estimation with a dipole-dipole pair, a dipole-loop pair, or a loop-loop pair of various orientations. Chapter 4 aims to estimate the polarization of fully polarized sources, given prior knowledge of the incident sources' azimuth-elevation directions-of-arrival, using a pair of diversely polarized antennas two electrically small dipoles, or two small loops, or one each. The pair may be collocated, or spatially separated by a known displacement. Each antenna may orient along any Cartesian coordinate. Altogether, fifteen antenna/orientation configurations are thus possible. For each configuration, Chapter 4 derives (i) the closed-form polarization-estimation formulas, (ii) the associated Cramer-Rao bounds, and (iii) the associated computational numerical stability.