| Due to its characteristics of all-day,all-weather,long-distance,and high-resolution,ISAR has been widely used in target detection,motion monitoring,identification of enemy and foe,and precision guidance of weapons.In recent years,the emergence of dual/multi-base ISAR imaging systems has greatly improved the concealment and anti-jamming ability of ISAR.At the same time,the In ISAR developed on the basis of ISAR can acquire the 3D geometric contour information of the target,which gives the ISAR the ability to accurately characterize and accurately identify its target.Therefore,whether in military or civilian applications,the application of ISAR will be more common.At the same time,the additional amplitude-frequency modulation of the echo components of the ISAR target in the ISAR target has also attracted people’s attention and named it the micro-Doppler effect.On the one hand,due to different factors such as motion form and motion parameters,the micro-Doppler characteristics of the micro-motion components are also different,which can be used as a prominent identifier for the target recognition classification.On the other hand,the motion law of the micro-motion component is quite different from that of the target body.During the ISAR imaging,the distance traveled by the unit is generally present,which causes the ISAR to fail to correct the motion and obtain the defocused two-dimensional distance-Doppler image.This feature brings new inspiration to the ISAR jamming technology.This thesis aims to propose a micro-motion jamming method for single-base ISAR,dual/multi-base ISAR and In ISAR by studying the micro-Doppler effect of radar targets.At present,the jamming methods for ISAR are mainly focused on the generation of deceptive jamming and coherent modulation suppression jamming with fixed-shape false targets.The jamming methods using the micro-Doppler effect are rare,for dual/multi-base ISAR and In ISAR.The method of micro-motion jamming remains to be studied.Therefore,the research content of this thesis supplements the micro-motion jamming method for various systems of ISAR at this stage,which provides a theoretical basis for the practice of ISAR confrontation and provides some new ideas for the development of imaging radar electronic countermeasures.The content of this article is summarized in the following five parts:The first part expounds the background of this paper and the significance of the topic.It summarizes the development of ISAR imaging and its countermeasure technology at home and abroad,and summarizes the research status of micro-Doppler effect.Then the basic theory of ISAR imaging technology is studied,including the characteristics of chirp signal,motion compensation algorithm and micro-Doppler feature analysis method.The second part establishes mathematical models for the common micro-motion forms of the five ISAR targets,including rotational motion,vibration motion,precessional motion,bird flapping motion and human walking motion,and analyzes the mathematical expression of various motion forms.The specific expression and characteristics of the micro-Doppler effact are verified by simulation experiments.The third part proposes three kinds of micro-motion jamming methods for single-base ISAR.The micro-motion jamming method based on the modulation and forwarding principle is that the jammer first calculates the phase modulation term and the scatter delay in the ISAR echo according to the micro-motion false target template,and then modulates the collected ISAR transmit signal to generate an jamming signal.And amplify and forward to the ISAR receiver.The jamming method can generate a micro-motion false target point according to the corresponding position of the false target template in the ISAR image,and the jamming effect can be flexibly adjusted,but the premise of the jamming effect is the known ISAR and the template coordinate information,and the defect is also proposed.Micro-motion scattering wave jamming method.This method also performs micro-motion modulation on the ISAR transmit signal,but the difference is that the jammer forwards the jamming signal to the target and then scatters to the ISAR receiver,so jamming can still be performed if the enemy radar position is unknown.In addition,the pulse convolution micro-motion modulation jamming is also proposed.The jammer achieves the effect of generating a micro-motion false target point by convolving a specific distance unit of the target echo,which has the advantage of simple implementation.Finally,the effectiveness of the three jamming methods is verified by simulation experiments.The fourth part proposes two methods of micro-motion jamming for bi-/multi-base ISAR.Due to the passivity and concealment of the receiving station,the bi-/multi-base ISAR can greatly reduce the influence of the conventional jamming method.A micro-motion scattering wave jamming method is proposed for this problem.The jammer will simulate the micro-motion false target point.The echo phase information is modulated to the ISAR transmit signal and then forwarded to the target.The multiple ISAR receiving stations can simultaneously interfere with the target scattered jamming signal.However,the calculation amount of this method increases significantly with the increase of the number of false target points.Therefore,an improved pulse convolutional scattering jamming method is proposed,which simulates the generation of false target points by using the delay pulse and the ISAR emission signal convolution.By controlling the law of delay variation,the position and variation law of the false target point can be controlled,thereby achieving a flexible jamming effect.Finally,the effectiveness of the jamming method is verified by simulation experiments.The fifth part proposes two jamming methods based on dual channel jammers for In ISAR.First,the micro-motion modulation jamming method is: calculating a pseudo target jamming phase in the baseline direction of each antenna of the In ISAR according to a preset three-dimensional pseudo target template,and simultaneously transmitting the jamming signal by using two jamming channels with different coordinates,and two jamming signals having a specific phase relationship.The jamming phase generated after the superimposition of the In ISAR antennas in the baseline direction is equivalent to the jamming phase of the false target template,thereby generating a three-dimensional jamming effect on the In ISAR.Then,the inter-frequency modulation jamming method is proposed.The two-channel jamming channel is used to perform sinusoidal phase modulation with different frequency and delayed forwarding.The jamming effect of generating false target points with time-varying coordinates is achieved.Finally,the effectiveness of two three-dimensional jamming methods is verified by simulation experiments. |
