Research On Jamming Technique Against Inverse Synthetic Aperture Radar

Inverse Synthetic Aperture Radar (ISAR) is a high resolution microwave imaging system. It has great prospects in target recognition, anti-stealth, astronomy and air traffic control etc. It is an important research direction in radar imaging area. ISAR imaging technique has been rapidly developed to accommodate to the increasingly complicated electromagnetic environment, consequently to challenge the ISAR countermeasure field. The research on jamming methods against ISAR is urgent and important.The ISAR imaging is a course of two-dimensional signals processing. So ISAR has advantage of high processing gain received signal and bring difficulties to the jamming technique. The dissertation proposes several jamming methods against ISAR range image and two-dimensional image. Primary work of the dissertation is summarized as follows:1. ISAR imaging principle and echo signal processing method are studied based on the rotational platform. The processing methods concerned with range imaging are presented, which include matched filtering and dechirp processing in range dimension. The similarities and differences between them are discussed and the problem of choosing range sampling rate is studied in order to reduce the range sampling rate. The processing methods concerned with azimuth imaging are presented in detail, which is FFT processing method. The principle of how the azimuth dimension obtains high resolving power is studied. The paper also discussed the azimuth signal processing gain.2. The dissertation proposes a jamming method named convolution jamming, which includes pulse convolution jamming and noise convolution jamming. The convolution jamming method can produce false targets deceptive jamming or noise cover jamming according to the different forms of convolution signals. And this kind of jamming method can obtain all or part of radar signal processing gain, so it can save the jamming power. The convolution jamming and the shift-frequency jamming are combined in order to improve the jamming effect; in other words, the combined jamming can produce jamming which is ahead of the target echoes.3. Several coherent jamming methods are proposed, which include noise weighted frequency modulation jamming, pulse weighted frequency modulation jamming, sawtooth weighted frequency modulation jamming and sinusoidal weighted frequency modulation jamming. The noise weighted frequency modulation jamming can produce cover jamming; others can produce both cover jamming and false target deceptive jamming. Some important parameters, jamming type determinants and jamming gain are discussed. Those jamming methods can utilize the radar signal processing gain, so they can save the jamming power.4. The dissertation proposes a pulse amplitude modulation jamming which uses pulse signal whose duty ration is50%. This kind of jamming can produce false target deceptive jamming effect. At the same time, it can solve the separation problem of the jamming receiver and transmitter. The pulse amplitude modulation jamming can also be combined with other kinds of jamming methods; thereby they can improve their jamming effect. The jamming principle, important parameters and the time-frequency characteristic are discussed. The jamming effect of the pulse amplitude modulation method and correlative combined jamming are discussed.5. For the reduction of sampling bandwidth, ISAR echoes are usually dechirped first in the receiver. A new method named range deceptive jamming is proposed in this chapter, which is based on the feature of dechirping. The narrow band pulse is jammed by range pull-off, and then radar obtains a false range value and produces a false reference signal. So the point-spread function (PSF) in the frequency domain will be widen or folded and imaging will be worsen or destroyed. Theoretical analysis and computer simulation justify the validity and efficiency of the new jamming technique.6. There are linear relation between the ISAR echoes and the azimuth position of target. So we can utilize the shift-frequency jamming and the coherent jamming methods to the azimuth imaging. Those methods are combined with the jamming methods countering range imaging to form two-dimensional jamming methods. The jamming principle, important parameters, the time-frequency characteristic and the jamming gain are all discussed. The two-dimensional jamming methods can produce both cover jamming and false target deceptive jamming.7. The dissertation discusses ISAR radar equation and jamming equation and studies evaluation of jamming effectiveness against ISAR. Since ISAR is a kind of two-dimensional imaging radar, target of which is extended and result of which is an image, it is necessary to evaluate jamming effectiveness against ISAR based on the image. The correlation coefficient can be used as a criterion to evaluate the jamming effect. Furthermore, the fuzzy mathematics is discussed.