A. E. Okhrimenko, N. G. Parhomenko, P. G. Semashko

The progress of radioelectronics infrastructure over the significant part of the Earth surface results in the existence of electromagnetic fields of various frequency ranges. The intensities of these fields are enough intensity to illuminate targets. Thus, the development of semiactive radars operating with broadband TV and radio transmitters - illumination is stimulated as well as the mobile base stations illumination. Their prime advantages are based on the absence of transmitter in the radar system. Thus, an absolute radio stealthiness is achieved, the assignment of radio frequency resource is not required, ill effect on the environment and people is reduced. Cluster topology allows detecting stealth aircrafts for they have bistatic scattering cross-section larger than the backscattering one. The methods of direct path interference suppression in semiactive radars operating with various non-radar illuminators are considered. Such measures as polarization rejection, electrodynamic shielding, spatial coherent autocompensation, demodulation with following spectral rejection, and time-and-frequency selection during correlation processing and its complex efficiency are analyzed. It is shown that the key point for all kinds of semiactive radars operating with various non-radar illuminators is the working range of -60 to -90 dB in the input signal-to-jam ratio. For the correct target detection with the probability of 0.9 and false alarm rate 10-5 the suppression of direct path signal with the efficiency of 80 to 110 dB is required. The conjunctive use of polarization rejection, electrodynamic shielding, spatial coherent autocompensation, demodulation with following spectral rejection, and time-and-frequency selection during correlation processing is necessary to provide the exact efficiency. The overall effectiveness of the abovementioned measures for typical illuminating signals provides the required suppression rate. It is possible to give up some suppression methods, like electrodynamic shielding when using the digital television signal DVB-T or base station signal, for it can increase the mobility of the semiactive radars.