O.S. Agafonov - Leading Engineer, JSC "MSDB "Almaz-Antey -
E.D. Anufrikov - Head of Department, JSC "MSDB "Almaz-Antey -
V.V. Vinogradov - Ph.D. (Eng.), Head of Department, JSC "MSDB "Almaz-Antey?. E-mail: finn-vvv@mail.ru
A.I. Danilenko - Dr.Sc. (Eng.), Head of Special Design Bureau, STC "Altair" JSC "MSDB "Almaz-Antey?

A technique is presented for locking-on and tracking an object equipped with a transponder by a radar that has a modular phased array and a digital signal processor provided that the radar has a common echo-signal and transponder-signal receiver. It is necessary to take into consideration that the carrier frequency of the transponder signal (as opposed to the echo signal) may change due to instability of the transponder oscillator. This circumstance is essential when the transponder signal is processed by a receiver intended for processing the echo signal. A method that retrieves the object-s distance and angular coordinates is considered. The distance and angular coordinates are estimated during different phases of object-s flight using both the inertial navigation data and the results of radar processing of the transponder signal, taking into account that the signal contains a PSK signal. A technique for phase demodulation of the transponder signal using ADC samples is presented. The object distance is estimated based on the time position of the convolved PSK signal. The angular coordinates of the object are estimated by the maximum likelihood method. The angular errors are close to those characteristic of the monopulse radar. The distance errors are close to those of digital systems (approximately two sampling intervals) provided that the signal-to-noise ratio is no less than 20 dB.