Research On Key Technology Of Multi-beam Space Synthesis

High frequency ground wave radar has attracted the attention of researchers because of remote target detection and sea forecasting.Its application of engineering technology is also increasingly mature.However,covering a large area,the enemy is easy to attack the target.The impact of clutter on its target detection is a key factor that plagues its further development.The existing high-frequency ground wave radar signal transmission direction fixed,can't be flexible control.In this paper,we study the problems encountered in the two cases of single beam and multi-beam space synthesis,and put forward the corresponding solutions to these problems.In order to completely cover the airspace,a single beam is sequentially emitted in all directions.The amplitude of the echo signal has a significant periodic change,which produces Doppler blur in the Distance-Doppler processing.When the array parameters are fixed,the carrier frequency range of the aircraft and the ship's target which does not appear Doppler blur is given.Compared to omnidirectional radiation,the performance of the emitted single beam in azimuth resolution is improved.The transmission multi-beam spatial synthesis can simultaneously emit a specific signal in multiple directions specified in the space.Two methods of transmitting multi-beam are analyzed.Fourier transform is used to generate the phase,and the calculation is faster,but the phase is fixed in particular direction.A space-time orthogonal coded signal is used to transmit multiple beams.The space-time orthogonal code set is constructed by algebraic method,simulated annealing algorithm and genetic algorithm.The algebraic method has the fastest coding rate,but the symbol length is fixed.Simulated annealing algorithms and genetic algorithms produce equivalent performance of orthogonal codes.But Genetic algorithm converges faster.The autocorrelation side lobe and the cross correlation peak decrease as the symbol length increases.With the increase in the number of sequences both of them didn't change significantly,which also indirectly shows the robustness of the two methods.They are reduced with the increase in the number of phases.Compared with the three kinds of echo processing methods,the first Distance Doppler processing has the same effect with the first beam forming.But the latter is less computationally.After mixing,the computational complexity of the distance Doppler process is minimal,but it is influenced by the performance of orthogonal coding.The actual situation is dif-ficult to produce the ideal space-time orthogonal coding signal,so the use of it is limited.The space-time orthogonal code signal has a higher distance sidelobe.The use of a convex optimization toolbox produces a mismatch filter,compared to a matched filter,where the sidelobe is significantly reduced.The influence of amplitude-phase error on the sidelobe and pointing of the transmitted beam is analyzed.The error of the channel is estimated and corrected by the synchronization orthogonality of Walsh code.As the SNR increases,the estimation error is closer to the real error.At the same time in the far field conditions,the antenna error is estimated and corrected.