Research On High Precision Direction Finding Method Of Secondary Radar Signal

For general signals,the Direction of Arrival(DOA)estimation algorithm has been extensively studied,but for signals with special waveforms,the traditional DOA estima-tion method cannot achieve the optimal DOA estimation performance.Compared with the primary radar signal,the secondary radar signal transmits information in the form of short-time pulses,and its signal format is more complicated.The traditional DOA estima-tion method is difficult to meet the DOA estimation needs of the secondary radar signal.The thesis aims at the DOA estimation problem of a typical secondary radar signal—Identification of Friend or Foe(IFF)signal.Starting from the signal format,the different situations of IFF preamble pulse and IFF data pulse are studied respectively.The pro-posed algorithm can improve the DOA estimation accuracy of IFF signal under restricted conditions.The main contents are as follows:1.Starting from the signal model of IFF signal,the signal characteristics,working modes and signal format of secondary radar signal are introduced in detail.The thesis sorts out and analyzes the different types of IFF signal waveforms,and briefly derives the theoretical performance bounds under different signal models.2.In the case that the waveform of IFF preamble pulse signal is known,use decou-pled maximum likelihood(MLE)method to find direction,and compare with traditional beamforming(CBF)method under the unknown waveform.The simulation experiment results show that the known signal waveform can improve the DOA estimation accuracy of IFF preamble signal.3.The thesis proposes a demodulation-reconstruction method in the case that the waveform of IFF data pulse signal is unknown and its modulation parameters are known.This method makes full use of MSK modulation parameters through the demodulation-reconstruction process,so that the root mean square error(RMSE)of IFF data pulse signal DOA estimation is lower than the direction finding RMSE of CBF method,and the DOA estimation result of the decoupled MLE method can be approximated when the signal-to-noise ratio(SNR)is high.4.The thesis proposes an IFF direction finding method based on joint demodulation for the situation where the partial waveforms of IFF signal are known.This method first identifies the signal type of the received signal and extract the start-end points of pulse waveform,then handles preamble pulse and data pulse signals separately,and finally uses the reconstructed waveform to complete the DO A estimation of IFF signal.Through sim-ulation experiments,the effectiveness of the direction finding algorithm based on joint demodulation is verified.Under a high SNR,the DOA estimation result based on the pro-posed algorithm can approximate that of known signal waveforms and unknown complex amplitudes case,which can meet the requirements of high-precision DOA estimation.