This article discusses the issues of increasing the noise immunity of semi-active radar systems based on the use of transmitters for target illumination using harmonic radiation and remote Doppler receivers in conjunction with a central information processing station. This solution is not only the simplest from the point of view of hardware implementation, but also has such advantages as high speed and increased sensitivity, as well as the ability to search-free spatial and frequency processing of radiation. Of the shortcomings, it should be noted the low secrecy of the functioning of this semi-active radar system. The purpose of the work is to eliminate the indicated drawback by using frequency tuning in the illumination transmitter or when using several spaceseparated illumination transmitters operating according to a given frequency-time scheme in a semi-active radio-location system. In addition, the paper deals with the optimization of the main parameters of portable Doppler receivers of semi-active radar systems. In particular, the paper gives recommendations for reducing the blinding effect of a direct signal to a Doppler receiver and presents a set of measures aimed at increasing the range of action of semi-active radar systems up to forty kilometers. In this paper, we consider the case of operation of a semi-active radiolocation system operating in a limited spatial sector using one remote receiving point. The illumination transmitter, which is usually placed on a high-rise object, generates directional radiation, intended primarily for solving various tasks in the field of telecommunications, for example, providing mobile communications, relaying satellite information, etc. In this system, the illumination transmitter is used in as a signal generator for illumination of air targets
