| Different from traditional phased array radar,which transmits the same waveform in each channel,each transmit channel of the frequency diverse array radar introduces a small frequency difference in the order of pulse repetition frequency.Therefore,the signal waveform transmitted by each channel is different.Each channel of the new radar increases the degree of freedom of frequency diversity,its transmitting pattern has the characteristics of time range angle three-dimensional dependence,which brings new degrees of freedom of signal processing.It has great application potential in resolving range ambiguity,anti-main lobe interference,joint estimation of angle range parameters and so on,so it is widely concerned by many scholars.However,frequency diverse array is a multi-channel array radar system,and there must be system error,which mainly include antenna-level error and RF component-level error.The existence of system error will lead to the degradation or even complete failure of antenna beamforming performance,and it is easy to be affected by temperature,humidity and other environmental factors,showing the characteristics of slowly changing with time.Therefore,it is necessary to study the real-time calibration technology of the frequency diverse array system error.As a new system radar,the frequency diverse array radar uses frequency diverse freedom to tap the potential of the system and puts forward higher requirements for system error calibration.In view of the above-mentioned problems and requirements,the key technologies study for the frequency diverse array radar system error estimation and calibration,combined with the system error calibration of the receiving/transmitting beamforming has been carried out in this thesis.Its main work is summarized as follows:1.Without considering the system error,the frequency diverse array radar signal model and transmitting-receiving beamforming algorithm are introduced.Firstly,the uniform linear array signal model of the frequency diverse array radar is described in detail.Secondly,the basic principles of frequency diverse array beamforming under continuous signal and pulse signal are derived on the basis of this model.Then,the simulations of frequency diverse array and phased array beamforming are carried out.Finally,through the comparison of simulation results,the conclusion that the frequency diverse array transmitting pattern has the three-dimensional dependence of time distance angle is verified.2.Aiming at the defect that the traditional channel mismatch model does not have the group delay parameter,the in-band group delay parameter is introduced to construct an improved multi-channel broadband mismatch model.Firstly,in order to improve the accuracy of characterizing the actual channel mismatch,a multi-channel wideband mismatch model with in-band group delay parameters is constructed.Secondly,on the basis of this model,a variety of calibration methods are introduced from the perspective of time domain and frequency domain,and the evaluation criteria of calibration performance are described.Then,the simulation results verify the bad influence of the improved mismatch model on the frequency diverse array radar transmitting pattern,which caused the beam pointing offset and the main sidelobe ratio reduction.Finally,the simulation results show the effectiveness of the proposed method.3.In response to the need for real-time estimation and calibration of the frequency diverse array radar system error in self-developed engineering applications by our team,a fast calibration scheme of multi-channel internal and external fields combined with separation of transmitting and receiving is proposed.Firstly,the design block diagram of the selfdeveloped radio frequency component system in engineering applications is given,and the sources of system fixed and random error are analyzed and determined.Secondly,according to the error source and the system design model,a fast calibration scheme of multi-channel internal and external fields combined is proposed.Then,the detailed steps of this proposed scheme are described,and two different reference channel selection methods are expanded based on the scheme.Finally,t the simulation results show that the multi-channel internal and external field combined calibration scheme has the advantages of better performance and faster speed.4.Based on the self-developed frequency diverse array radar hardware platform by our team,multiple modules of the timing board and the transmitting board sub-system are designed and developed independently,such as the network communication,timing generation,waveform generation and preprocessing.Firstly,the system composition,overall framework and respective subsystem functions are described in detail.Secondly,the block diagrams of timing board and transmitting board are introduced,and the experimental reports and test results of some key modules are given.Finally,it lays the foundation for the admission data of the field joint test,and provides effective engineering support for the frequency diverse array hardware implementation.5.Based on the self-developed frequency diverse array radar hardware platform by our team,the system function through field joint test is verified,and the measured data is processed.Firstly,the purpose of the outfield joint test is introduced in detail.Secondly,the detailed steps and operation flow of outfield joint test are given.Finally,through the processing and analysis of multiple sets of field tests and the current existing measured data,the inconsistent and time-varying characteristics of amplitude and phase error between channels are verified,and the feasibility and convenience of the proposed scheme in engineering application are further proved.Based on the theoretical study of transmitting-receiving beamforming algorithm for new system frequency diverse array radar,this thesis analyzes the influence of multi-channel mismatching on beamforming performance.According to the actual engineering application requirements,a fast calibration scheme with better performance and more convenient combination of internal and external fields is proposed,which is of great significance for subsequent hardware development,error correction and beamforming. |
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