Space-Time Two-Dimensional Signal Processing Method For Airborne Conformal Array

The conformal array antenna can be installed on various aerial platforms.It can save space,reduce weight,reduce air resistance,minimize the influence of the antenna on the aerodynamic performance of the aircraft,and expand the scan range of the antenna beam.The conformal array antenna has attracted the attention of researchers in the field of airborne radar with its unique advantages.The special geometric configuration,platform motion,and other external environmental changes cause the statistical properties of clutter to be more complex than those of planar arrays.The clutter spectrum shows not only a significant non-stationarity in distance,but also a serious broadening in the Doppler domain.The non-stationary properties are also exhibited in the array element domain,which results in a serious degradation of the performance of the space-time two-dimensional signal processing(STAP)method that is suitable for the conventional planar array.Therefore,it is of great significance for the application of the conformal array in airborne radar to carry out research on the airborne 2D signal processing method of the conformal array.In this thesis,based on the application of the conformal array in airborne radar,the signal processing method in the traditional planar array is used to carry out the space-time processing method of clutter suppression.First,the clutter signal model is established for the planar array and the conformal array,and the clutter characteristics are studied.Secondly,the compensation algorithms for the clutter non-uniformity of several planar array airborne radars are studied and applied to the conformal array.The applicability is discussed,including DW algorithm,ADC algorithm,multi-space azimuth compensation algorithm and pitch pre-filtering algorithm,robust pitch pre-filtering algorithm in the case of distance ambiguity,and a conformal array Multi-space azimuth compensation algorithm is proposed;Finally,for the problem of mismatch between steering vectors and data caused by the mutual coupling effect of conformal arrays,two open-loop mutual coupling compensation methods are proposed.The main work of the thesis is summarized as follows:1.Space-time two-dimensional signal processing method for plane array airborne radar and its applicability in conformal arrays.A brief analysis of the space-time processingtechnology and dimensional-reduced space-time processing technology was performed,and the simulation verified the effectiveness of the STAP technology.In order to solve the problem of distance dependence of clutter spectrum of airborne radar with low pulse repetition frequency,three local compensation algorithms are studied in this thesis,and the simulation results verify the effectiveness of spectral compensation and point out that multi-space azimuth compensation algorithm is superior to DW algorithm and ADC algorithm,and the applicability of these three algorithms in the conformal array are analyzed and discussed in depth;for the problem of range ambiguity in the echo signals of airborne radars with medium and high frequency pulse repetition frequencies,this thesis studies the pitch angle of freedom.The pre-filtering algorithm,but the algorithm has a high requirement for the accuracy of the ground clutter pitch angle.When there is an error in the height of the carrier,the effect of pitch pre-filtering will be affected,therefore,a robust pitch pre-filtering algorithm is studied in this thesis,and the sensitivity of the algorithm to the height error of the carrier is reduced.Finally,the applicability of the two algorithms in the conformal array is analyzed and discussed in depth.2.Space-time two-dimensional signal processing method for conformal array airborne radar.Based on the idea of plane array airborne radar clutter spectrum compensation algorithm and the variation of space-time distribution of airborne radar clutter with distance and array element number,a multi-space orientation compensation algorithm for conformal arrays is proposed.Each Doppler channel clutter of each training sample performs spatial angular frequency shift along the space angle of the same Doppler channel clutter along the spatial azimuth of the unit to be detected.As a pre-processing method before space-time processing,the results confirmed that the spectrum of clutter in the side lobe area was reduced and the minimum detectable speed was improved.3.Co-array airborne radar space-time two-dimensional signal processing mutual coupling compensation method.In this thesis,it is theoretically analyzed that the space-oriented vector of the planar array will produce the mismatch problem of the steering vector when it is affected by the mutual-coupling matrix,and the spatially-oriented vector of the conformal array is affected by both the mutual-coupling matrix and the array element pattern,and more serious mismatch problems will result.The mutual coupling effect changes the array flow pattern and the beamforming characteristics,resulting in a larger blind zone of the main lobe clutter in the Doppler domain.Aiming at the problem of mismatch between spatially steered vectors and data in conformal arrays,two open-loop mutual coupling compensation methods are proposed in this thesis.One is the steering vector compensation method,and the mutual coupling compensation is performed on the ideal steering vector when the echo data is determined.The other is data compensation method,and the mutual coupling compensation is performed on actual echo data.These two methods effectively compensate for the effects of mutual coupling effects and achieve theoretically better performance.