THE METHODS OF PROTECTION FROM THE PULSE DRFM JAMMING
Authors: Atamanskyi D. V. , Riabukha V. P. , Vasylyshyn V. I. , Semeniaka A. V. , Katyushyn E. A. , Stovba R. L. 
Published: December 2024

Context. The repeater reusable pulse jamming like DRFM (Digital Radio Frequency Memory) significantly complex the radar situation for radar with LFM probing signals. Besides of the marks from the existing targets the other marks are arising on the radar PPI-screen that simulate analogous to them false targets. The known methods of struggle with the repeater reusable pulse jamming like DRFM are inefficient that caused by specificity of the jamming. The synthesis of the methods of the struggle with such jamming is the actual problem
Objective. The estimation of possibilities of the known methods of noise immunity for reduction of the negative influence of pulse jamming like DFRM on the processing of the useful signals and suggestion of the alternative method of LFM signal processing on the DFRM jamming background.
Method. The efficiency of the methods is defined experimentally on the results of simulation and comparison of them with the known results presented in the literature
The results. The inefficiency of the known methods of protection from repeater pulse jamming for reduction of the negative influence of DRFM jamming on the processing of the signal reflected from the target is justified. The character of negative influence of DRFM jamming on the processing of the signal reflected from the target is defined. These jammings can create as masking effect as imitate the marks from the non-existing targets. It is shown, that device with two-side amplitude limitation on the input of compression filter which traditionally used for suppression of repeater pulse jamming is inefficient for suppression of DRFMjamming.
It is shown, that as compression filter for LFM signals with small base the filter matched with big base LFM signal can be used. However, these matched filters are not designed for LFM signal with small bases.
The conditions of matched filtration of small base pulse LFM signals in the filters matched with big base signal are defined. The sufficient condition of the matched filtration of small base signal is coinciding of their phase frequency characteristic with corresponding area of the phase frequency characteristic of the big base signal. This fact explains the effect of forming of the maximums on the output of compression filter for pulsed of DRFM jamming and the effect of forming of false marks from targets
It is shown that limitation of the level of signals before their processing in the compression filter remove the energetic advantage of lamming above useful signal, however, do not influences in the form of phase frequency characteristic of jamming. This detail of the amplitude limiter is the reason of ineffective processing of the useful signal on the background of DRFM jamming in the devices like amplitude limiter-compression filter.
The method of suppression of repeater pulse jamming is proposed. The natural assumption about correspondence of powerful samples of the input mixture to jamming samples is on the base of this method In the case of digital processing this can be realised by nullifying the samples which are above the defined level of limiter. It is shown that processing devices, which uses such limitation, provides the effective processing of the useful signal on the background of DRFM jamming.
Conclusions. The scientific novelty of the obtained results is in the further development of practice of noise immunity of the radar with LFM probing signal, specifically the device that detects the reflected signal on the background of the repeater pulse jamming is proposed. The practice of matched filtration of complex signals obtains the further development, namely, the conditions of matched filtration of LFM signals with small base in the filters matched with the signals with big bases are determined. The sufficient condition is the coincidence of phase frequency spectrum of the small base signal with corresponding area of phase frequency spectrum of the big base signal.
The practical importance of investigation is that the processing device is proposed. This device provides the value of correct detection of the signal reflected from the target approximately twice as much to the known processing devices in the most cases.