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Amplitude monopulse direction finding in adaptive phased arrays

Keywords:

S. V. Petrov – Post-graduate Student, Leading Engineer, AO “VNIIRT” (Moscow) E-mail: petrovsv@list.ru


Implementation of the method of monopulse direction finding in the adaptive phased antenna array, forming nulls in the directions of sources of interference, encounters difficulties associated with the distortion of the direction-finding characteristics. One possible solution of this problem is the correction of offset and slope of direction-finding characteristics. In this paper we solve the problem of finding the offset and the slope correction coefficients for the case when only amplitudes of output signals from the partial beams of direction-finding bunch are available. These values are derived from following conditions – when direction of the steering of the antenna coincides with the true target di-rection, azimuth (Δu) and elevation (Δv) estimates expectation should be zero, and the corresponding direction-finding characteristics have a slope which is equal to one. As an example the five-beam direction-finding bunch consisting of the central beam, two beams, displaced in azimuth, and two beams, displaced in elevation is taken. The signals at the output of these beams are formed as a result of scalar multiplication of the weight vectors with the vector of the outputs of the antenna array elements. In the derivation of the expressions the assumption is used that the signal to noise ratio (SNR) is much greater than 1. This assumption is motivated by the fact that the monopulse direction finding method is applicable only for sufficiently high values of SNR. As a result the expressions for the elements of offset vector and slope matrix of direction-finding characteristics are derived. The derived expressions allow monopulse direction finding for arbitrary, including adaptive, weight vectors. When changing the interference environment, adaptive weight vectors are updated, which requires a corresponding recalculation of the correction coefficients of offset and slope of direction-finding characteristics. To illustrate the correctness of the expressions obtained and efficiency of the approach the mathematical simulation for the square 64 element antenna array is carried out. For several jamming scenarios cross sections of the direction-finding characteristics and vector diagrams of shifts of monopulse estimates for the various target directions are drawn. The obtained results demonstrate that the ap-plication of the proposed method of direction-finding characteristics correction allows to minimize systematic errors of estimating the target coordinates in the adaptive phased array.
References:

 

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