I.V. Kryuchkov – Head of Department, SRI of Radioelectronic Technics of Bauman Moscow State Technical University E-mail: kryuchkov @bmstu.ru

M.I. Noniashvili – Ph.D.(Eng.), Associate Professor, Department RL-1, Bauman Moscow State Technical University E-mail: min-st-1986 @mail.ru

G.P. Slukin – Dr.Sc.(Eng.), Senior Research Scientist, 

Director of SRI of Radioelectronic Technics of Bauman Moscow State Technical University

E-mail: niiret@bmstu.ru

V.V. Chapursky – Dr.Sc.(Eng.), Senior Research Scientist, Main Research Scientist, 

SRI of Radioelectronic Technics of Bauman Moscow State Technical University E-mail: valch2008@yandex.ru

The methods of the target’s altitude measuring in the centimeter radar with phased antenna arrays (AA) based on subarrays at the observation of low-flying air objects over the earth and water surface are considered. The analytical formula for the generalized correlation integral is used for the calculation of topographic bearing diagrams on the coordinates of the horizontal range and the altitude of the low-flying target above the surface level.

Examples of the AA with an equidistant arrangement of the subarrays and nonius AA with the displacement of the upper and lower rows of the subarrays in the C-band radar when observing low-flying targets in the presence of the antipode are investigated. The bearing diagrams in the plane of target’s «range–altitude» are compared, and the dependences of the target’s altitude estimates on the range at different altitude of the target flight and the reflection coefficients from the surface are found.

For example of the equidistant AA on the two-dimensional bearing diagrams the maxima corresponding to the antipodes are visible. The maxima are shifted below the coordinates of the antipode, while the estimates of the target’s altitude themselves are also shifted above their true values, which is due to the influence of the antipode. According to the topographic bearing diagram analysis, the estimates of the target’s altitude were found and it was seen that with the change in the target’s altitude in the interval of 10…40 m, the boundaries of acceptable errors in the altitude as the function the range grow equally with the altitude increase at the reflection coefficients of 0.5 and 0.8. With increasing distance of the target above a certain limit there is a significant increase of systematic errors of the altitude estimation, which is periodic in nature and comparable with the true height of the target.

For the example of the nonius AA, it is established that for the target ranges of not more than 1000 m, the antipode and target marks are resolved and are at the correct heights, in contrast to the case of equidistant AA. When the target range is more than 1000 m, the antipode and target marks actually join, at least in the range of height estimates of 50…+50 m. Transition from equidistant AA to nonius AA in these examples leads to a significant reduction in the systematic errors of the target altitude estimate, as well as to the expansion of the range intervals at which these errors do not exceed 10…20% of the true altitude of the target.

The generalization of the analysis of the nonius AA should be aimed at optimizing the placement of the nonius subarrays to meet the design and technical requirements for the placement of the subarrays and AA in general, as well as the requirements from the processing system and data transfer to radar using nonius AA. The result may lead to a further reduction in the systematic errors in the estimation of the low-flying target’s altitude.

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