Browsing by Author "ZOLTOWSKI, MD"

Now showing 1 - 3 of 3

BEAMSPACE ML BEARING ESTIMATION INCORPORATING LOW-ANGLE GEOMETRY
(1991-05-01)
ZOLTOWSKI, MD
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
A problem of interest in low-angle radar tracking is that of bearing estimation in the presence of a strong specular multipath component that arrives within a beamwidth of the direct path signal. Three-dimensional beamspace domain maximum likelihood (3D-BDML) is a computationally simple ML bearing estimation algorithm applicable in this scenario which operates in a 3-D beamspace. A variation of 3D-BDML incorporating the multipath geometry as a priori information is presented. In symmetric 3D-BDML the pointing angle of the center beam is equal to the bisector angle between the direct path ray and the image ray, which may be estimated a priori given only the radar height and the target range. The effect of the inclusion of a priori information on the performance of 3D-BDML is analyzed in terms of the dependence on the relative phase difference between the direct and specular path signals, the sensitivity to error in the bisector angle estimate, and the results of operation when no specular multipath component is present in the data. In addition, computationally simple schemes for coherently incorporating multifrequency data into 3D-BDML are investigated as well.
BISECTOR ANGLE ESTIMATION IN A NONSYMMETRIC MULTIPATH RADAR SCENARIO
(1991-12-01)
ZOLTOWSKI, MD
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
In the classical problem of low-angle radar tracking, echoes return to the array via a specular path as well as by a direct path, with the angular separation between the two ray paths a fraction of a beamwidth. The performance of any bearing estimation scheme in this scenario is dependent on the phase difference between the direct and specular path signals at the centre of the array. The beamspace domain maximum likelihood (BDML) bearing estimator is a recently developed three-beam extension of the sum and difference beam technique employed in conventional radar. Nonsymmetric BDML breaks down when the phase difference is either 0-degrees or 180-degrees. In contrast, symmetric BDML, in which the point angle of the centre beam is the bisector angle between the two ray paths, can theoretically handle any phase difference, with the 0-degrees case giving rise to the best performance. A simple, closed-form bisector angle estimator is developed based on characteristic features of the 3 x 3 forward-backward averaged beamspace correlation matrix when the centre pointing angle is the true bisector angle. In this way, a 2-D parameter estimation problem is decomposed into two successive 1-D parameter estimation problems: estimation of the bisector angle, followed by estimation of the target bearing. Simulations are presented assessing the performance of the new bisector angle estimator and comparing the performance of symmetric BDML employing the new estimator with other ML based bearing estimation schemes in a simulated low-angle radar tracking environment.
INTERFERENCE CANCELLATION MATRIX BEAMFORMING FOR 3-D BEAMSPACE ML/MUSIC BEARING ESTIMATION
(1991-08-01)
ZOLTOWSKI, MD
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
In conventional monopulse radar, the bearing of a single target within the mainlobe of the transmitted beam is estimated via a ML procedure based in a 2-D beamspace defined by sum and difference beams. For the case of two closely spaced targets angularly located within the mainlobe of the transmitted beam, 3D-BDML is a computationally simple ML bearing estimation scheme which operates in a 3-D beamspace generated by three orthogonal, classical beamformers. The presence of strong interferers angularly located outside the mainlobe encompassing the two targets of interest necessitates the use of adaptively formed left, center, and right beams. Let M denote the number of elements comprising the array. Novel procedures are developed for the construction of an M x 3 interference cancellation matrix beamformer which retains those properties of the M x 3 classical matrix beamformer critical to the computational simplicity of 3D-BDML. The most important of these is commonality of M - 3 nulls among the left, center, and right beams. Simulations are presented demonstrating the excellent performance of both single frequency and multifrequency 3D-BDML incorporating interference cancellation in a simulated low-angle radar tracking environment.