Research On DBF Method For Ultra-wideband Signal Space-Time Conversion

Ultra-wideband(UWB)radar has high range resolution,high ability in target recognition and the great capability of ECCM,which plays an important role in many scenes.However,since the bandwidth of UWB signal is large,the traditional narrowband signal DBF method is no longer applicable,so it is necessary to find a new method to solve the problem of UWB signal DBF.This thesis focuses on the DBF method of UWB signal based on space-time conversion.The DBF method need to converting the spatial signal accepted by circulating time-delay array to a time-domain signal,therefore,DBF process can be accomplished through time-domain convolution based bandpass filtering instead of spatial filtering,which avoids the beam pointing offset and the degradation of range resolution caused by the aperture fill phenomena of UWB signal.In addition,a single RF channel is used to receive the signals from array elements,which avoids the amplitude and phase errors between the channels and reduces the hardware cost of the antenna system.The main work of this thesis is as follows:First of all,this thesis analyzes the performance and problems of the existing single-channel DBF method,and gives the signal model for the realization of single-channel DBF by ultrawideband radar under the circulating time-delay coded array(CTDCA)and the space-time coded array(STCA).In order to solve the problem of high sidelobes caused by singlechannel reception under the STCA structure,an ultra-wideband signal single-channel DBF method based on space code agility is adopted,and the sidelobe level can be effectively reduced by using irrelevant space codes in different pulse repetition intervals and integrating DBF outputs of multiple PRIs.Secondly,the existing single-channel DBF method achieves the DBF process through timedomain filtering at the receiving terminal.In ultra-wideband cases,time-domain convolution based DBF will suffer from a mismatch between the sampling rate of the recorded signal and the array system response function.To solve this problem,this thesis gives a frequencydomain equivalent DBF algorithm based on the space code agility-based space-time coded array(SCA-STCA).This algorithm is immune to the mismatch between the sampling rate of the recorded signal and the space-time response function of the SCA-STCA under ultrawideband circumstances by constructing a frequency domain response function that can be generated accurately.It can also avoid the beam distortion caused by the mismatch of the sampling rate.In addition,the target motion compensation is taken into account in the development of the frequency-domain DBF algorithm,which can avoid the performance degradation of DBF caused by the target motion.Numerical simulations verify the effectiveness of this algorithm.Finally,the circulating time-delay array is used for transmission,each array element transmits the same reference signal at a certain time interval,and the time-frequency-space coupling characteristic of the delayed transmission signal is used to realize the array beam scanning of the specified range in a single pulse.Within one signal pulse,time beam scanning is equivalent to frequency beam scanning.Therefore,at the array at the receiving terminal,the signal can be received through a single array element and a single RF channel,and through a frequency-domain band-pass filter to obtain an echo signal at a specified angle,thereby achieving DBF process.The delayed reception structure of the array corresponds to the delayed transmission structure,which is more flexible in actual use,and its beam control is easy,and the engineering implementation is relatively simple.