Adaptive Waveform Design For Cognitive Radar System

Adaptive optimization of waveform design for cognitive radar is a frontier topic in recent years and is a research hot spot not only in China but also in other countries.This paper is mainly about under the background of the rapid development of the radar electronic technology,combined with cognitive radar application demand,how to research on the scene and target characteristics oriented cognitive radar waveform design theory and method.This algorithm can bring the radar system from the detection oriented sensor to the cognitive microwave sensor with the adaptive ability based on prior knowledge and feedback process.Traditionally,in order to realize the goal of radar optimal waveform design,we should set up corresponding measurement function for its received signal based on different applications.Different target,clutter and noise can lead to the different distribution of optimal waveform in the frequency domain.What?s more,the frequency distribution of optimal waveform under different transmit energy is also different.We can say that the classic waveform design algorithm is the basis of the radar to be “cognitive”.At present,with the rapid development of cognitive radar technology,its application is becoming wider and wider.These are big challenges for us.Optimal waveform-based multi-target detection problem is studied.The traditional radar waveform design method is established on the basis of single target,which limits the waveform design method in the application of the complex scene greatly.Different from the scene with single target,the scene with double targets and multi-target is much more complex.Under the basis of single target optimal waveform design method,we study the optimal waveform design algorithm facing to the multi-target situation so that the optimal waveform method can be used in the process of multi-target detection.In multi-target detection process,with the prior information,we estimate the clutter parameters so as to design the following waveforms.This optimal waveform based multi-target detection method can decrease the number of radar pulse significantly.Optimal waveform-design method facing with moving target is studied.For the present moving target detection/identification,the transmit signals used by the vast majority of MTI radars are fixed in its frequency form;in the meantime,basically all the waveform design algorithms are for stationary or static targets.This is a waste of radar performance.How to combine the waveform design algorithm with the moving target detection is a brand new subject.We try to detect moving targets using the optimal waveform method in this paper.Moving target oriented optimal waveform design process is given and waveform design based on static clutters or moving clutters is studied by us.Results show that under the condition of the static clutter and moving clutter,the optimal waveform designed to detect the same target is totally different.Our designed optimal waveform can increase SCNR and detectability significantly,which has a great effect.The SCNR-based two-dimensional matched filter problem for SAR system is studied.At present,the data acquisition,data processing and SAR image interpretation of SAR system are split with each other rather than united with each other.The application level of SAR data is significantly behind the development of the SAR system.It is the necessary way of the future SAR system improvement to combine the waveform design method with SAR system.In this article,we divide this combination into two aspects.On the one hand,aiming at special target or special scene,we discuss the designing of optimal SAR signals and its corresponding two-dimensional matched filter.In this paper,we focus on discussing the SCNR based SAR two-dimensional matched filter problem and designing the target-oriented optimal range matched filter and optimal azimuth matched filter based on different situations,so that the energy distribution towards target is “optimal” in two dimensional space.Waveform design problem and feedback optimization problem for cognitive SAR system are studied.For the conventional SAR systems,there is no direct relationship between the detection system and the scene to be detected,let alone the adjustment of the transmit signals cognitively based on the characteristics of the illumination scene.We focus on the waveform design and feedback process of SAR system.This new recursive SAR system with the capability of transmitting adaptive waveform can reduce the influence of clutter while SAR images are generated.Optimal transmitting waveforms are designed based on the estimated knowledge of the target and clutter in each azimuth direction.Clutter suppression filters are set to reduce the clutter response while maintaining most of the target response at each azimuth direction.With the above processes been down,the signal matrix is then filtered by traditional azimuth matched filter to obtain SAR image.The research in this paper shows that on the basis of cognitive theory and optimal waveform design method,we can optimize the whole process of radar data acquisition and image formation for the needs of different applications(detection,imaging,etc.)and different targets(single target,multi-target and moving target,etc.).The whole algorithm brings great benefits not only on the SCNR of the radar images,but also on special target detection/identification applications.It is no exaggeration to say that adaptive waveform design method for cognitive radar is the key to the new generation radar systems.