Research On Optimal Design Of Cognitive FDA-SAR Waveform

Synthetic Aperture Radar(Synthetic Aperture Radar,SAR)uses the relative movement between radar and target to synthesize small-size antennas into large antenna apertures,thus obtaining high resolution.At present,SAR has shown great potential in the fields of military reconnaissance,environmental monitoring and remote sensing mapping.However,the traditional working mode of SAR is relatively fixed,and it can not make flexible changes in changing targets,environments and tasks,which greatly limits the improvement of radar performance and the scope of application.Cognitive radar is a new type of interactive radar,which can form a closed loop between transmitter and receiver according to the target environment.The introduction of cognitive radar theory into SAR can realize the function of adapting the transmitting waveform of the transmitter by using the prior information and the feedback information in the echo,so that the radar has the ability to adapt to the electromagnetic environment and clutter background.Therefore,this paper takes the new cognitive FDA-SAR system as the research object,aiming at the cognitive waveform design problem of FDA-SAR,carries out the related optimization design research aimed at high-resolution imaging and clutter suppression.The main contents are as follows:(1)The related theoretical basis of FDA-SAR is introduced.Firstly,the array structure of FDA-SAR is given,the structure characteristics of radar and echo model are analyzed,and the receiving mechanism of FDA-SAR is introduced.Then a cognitive radar model based on FDA-SAR is established,the architecture and characteristics of the system are fully analyzed,the functions and technologies of each part of the cognitive system are defined,and the basic characteristics of cognitive waveforms and the relationship between cognitive waveforms and related parameters are analyzed.(2)Aiming at the high resolution imaging requirements of radar,the imaging resolution of FDA-SAR was analyzed first,and the optimization model based on the resolution ability was established to obtain the conditions that the radar transmitting waveform should meet when the imaging is optimal.Aiming at the detection requirements of radar in clutter environment,a transmitting waveform optimization function is established to maximize the signal-to-noise ratio of output terminal,and noise and noise suppression based on cognitive optimization is realized.Finally,the SCNR of receiver output was optimized by about 14 d B before and after the optimal waveform was detected.(3)Aiming at the need of high-resolution imaging capability and clutter suppression capability,the joint optimal waveform design method of integrated detection and imaging capability is studied.The objective function of joint optimization is established,the weight factor is set to adjust the optimization tendency of imaging and detection performance,and the final optimization waveform is obtained through the designed optimization search algorithm.The results of experimental simulation and data analysis on the optimized waveform show that the joint optimized waveform not only has the ability to suppress environmental clutter but also can maintain the high resolution imaging requirements.Finally,the optimized waveform was applied to FDA-SAR target imaging,and the imaging performance along the track and the tangent track was optimized by designing the frequency offset arrangement.The imaging results and performance evaluation analysis verified that the designed waveform was optimized in terms of imaging performance,resolution and clutter suppression.