Spatial Ring-Shaped Direction Finder Synthesis for a Source of Polarized Radio Emission
Purpose: Generalized approaches to the synthesis of radio direction finders (RDF) relative to receiving apertures are well-known and represented by various geometrical models. However, many particular practically important application cases require additional research, especially when the spatial polarization conditions of the radiolocation should be taken into account. One of such particular cases is the problem of biplanar passive RDF for a source of radio emission with an a priori unknown polarization parameters, implemented on a basis of a thin ring-shaped receiving aperture consisting of polarized antennas elements. This problem is actual for airborne combined active-passive radiolocation systems when the mentioned conformal receiving aperture of the passive part encircles the round active part antenna along its external edge. The goal of this paper is developing a biplanar RDF procedure for a source of polarized radio emission, performed by the passive part of a combined active-passive radiolocation system on the basis of a ringshaped antenna array of polar-sensitive elements, when the source signal polarization is uncertain. Methods: We use a modified optimal synthesis method for spatial multichannel radiolocation devices of primary detachment of the coordinate information, on the base of a likelihood function. The method is reasonably restricted to the spatial three-channel case. The synthesis problem is solved jointly for two angle coordinates of a polarized radio emission source, as their estimations are mutually dependent. The tighter is the polarization ellipse of the effective signal, the stronger this dependence reveals itself. Results: Certain dependences were obtained and analytically described for a ring-shaped antenna array, connecting the signal polarization parameters with the amplitude vector of the 3-channel receiving path response and with the coordinates of the three phase centers of the reception. On the base of these dependences, the correlations were obtained necessary to synthesize an RDF procedure for a polarized radio emission source with uncertain polarization. The result of the synthesis is a spatial 3-channel procedure of biplanar RDF being tuned to the radio emission source polarization in order to ensure that the two estimations of its angle coordinates are independent and optimal. Practical relevance: As an innovative technical solution, a procedure was proposed and grounded for passive biplanar RDF of a polarized radio emission source, implemented on the base of a ring-shaped array of linear polarized antenna elements. The procedure provides close-to-potential RDF accuracy for the passive part of a combined active-passive RDF system.