S. R. Heister, N. G. Parhomenko, A. S. Heister

Radar with television and radio designation technique has got practical progress in many countries over the recent years. Its major advantage lies in the absence of its own transmitter. It allows achieving absolute radio stealthiness, does not require the assignment of deficit radio frequency resource and there are no damage effects on environment ecology and on people. This kind of radars do not create antenna crosstalk, are cheaper in production and maintenance than active ones. High altitude of antenna elevation and the power of the broadband transmitters in use create suitable environment for detection of low or small targets. The main problems of radar system with extern designation are in the first place the selection problem of designation signal source guaranteeing acceptable radar characteristic and in the second place the suppression of background returns and direct signal if they exceed the friendly signal level by 60-90 dB. The results obtained in the paper allow solving the coherent compensation problem for frame spectral components of background returns and direct signal performed between filters in the semiactive radar with television designation. It is shown that the clutter frame spectral components (of both background returns and direct signal) in semiactive radar are located in zone of potential Doppler frequencies of friendly signals, reflected from target. Presence of the clutter spectral components leads to significant decrease of detection range of small aircraft. Usage of traditional rejector filters tuned to the frequencies of the frame components leads to appearance of "dead" zones for velocity. New method of clutter frame spectral component coherent compensation based on amplitude-shift keyed signal features and signal subtraction performed between filters with adaptation to the phase relations of the spectral components of clutter is presented.