In order to better suppress the complex electromagnetic interference faced by synthetic aperture radar, it is necessary to understand the mathematical models of various interferences reflected in the received signals of synthetic aperture radar, and better design targeted interference suppression algorithms according to the mathematical models of different interference signals.
Suppress interference; Deception interference; active jamming
What are the signal models of deception jamming and suppression jamming?
According to the relative bandwidth and modulation mode of jamming signal, suppression jamming can be divided into three forms: narrowband jamming, FM broadband jamming and sinusoidal modulation broadband jamming.
Among them, * represents the scattering coefficient of jamming, the SAR signal intercepted by jammer, and represents convolution operation and Dirac function. At the same time, part (a) represents amplitude scaling, which is usually obtained according to the prior information of the real scene, and parts (b) and (c) respectively represent time delay and Doppler modulation, both of which are related to the instantaneous tilt distance from the jammer to the false target, and can be expressed as
(9)
Where represents the instantaneous tilt distance of the false target. Assuming that the action time range of the jammer is, the range pulse compression signal of the false target scattering point at the same position can be expressed as
( 10)
Among them, there is r'? () indicates the scattering coefficient and instantaneous slant distance of the scattering point of the false target respectively. Comparing the expressions of false target scattering point and real scattering point, the main difference lies in supporting time domain and Doppler phase, except for the change of amplitude. The relationship between them can be expressed as follows
( 1 1)
The schematic diagram of time-frequency distribution of deception jamming and real echo is shown in Figure 2. According to the different jamming effects, deception jamming areas can be divided into:
(1) Strong jamming area: 1 Deception jamming in shadow area partially coincides with the echo of synthetic aperture radar, so it is difficult to suppress it effectively by conventional methods, thus forming strong deception jamming in the imaging results of synthetic aperture radar, which is the most harmful;
(2) Weak interference area: Deception interference in shadow area 2 does not coincide with the echo of synthetic aperture radar in time-frequency domain, and its Doppler spectrum does not exceed the azimuth bandwidth defined by the pulse repetition frequency of synthetic aperture radar system. Deception interference in this area is easily suppressed;
(3) Interference failure zone: The deceptive interference in shadow zone 3 is aliased because it exceeds the limit of Nyquist sampling theorem. Although it can't form an effective false target imaging result, it will still reduce the imaging quality of the real scene in the form of noise interference.
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