| TACAN navigation system is a polar coordinate navigation system,which belongs to shortrange radio navigation.It has the advantages of high precision,small size and flexible deployment.It can provide users with two services of direction measurement and distance measurement,and has been received by the armies of many countries.It is widely used in the navigation of carrier-based aircraft and fighter jets in NATO and third world countries.Therefore,the electronic reconnaissance of TACAN signals in electronic warfare is of great value.This thesis mainly studies the third-party detection of the TACAN signal,the baseband repeated frequency signal deinterleave,the pulse type identification,the envelope frequency extraction,the identification of the TACAN signal and the azimuth solution of the TACAN signal.According to the frequency range of TACAN signal and the characteristics of multichannel and narrow-channel,IF sampling is adopted,and a detection scheme of two-stage channelized reception is designed.The first-level channelization divides the entire frequency band to be received,including the TACAN band,into four channels and moves them to the baseband.The second-stage DDC obtains a zero-IF signal after mixing,and uses a polyphase structure FIR decimation filter to filter out the IF signal,leaving only the baseband signal.Measurements of time domain parameters are performed on baseband signals.After the receiver is processed and the time domain parameter is measured,the signal is sorted.The pulse form of the TACAN signal has a fixed envelope frequency and is a standard specification.Therefore,this thesis uses the PRI-based repetition frequency signal sorting method to focus on the PRI sorting of the TACAN signal.Firstly,pre-selection is carried out according to the time domain parameters RF,PW,etc.of the baseband signal,and the pulse signals with different parameters from the TACAN signal are eliminated.For the remaining repeated frequency signals,the cumulative difference histogram(CDIF)method and the sequence difference histogram(SDIF)method was used for sorting.The simulation results show that the TACAN reference pulse and identification pulse can be sorted out effectively.Use the pulse amplitude to restore the baseband envelope,improve the envelope through smoothing and interpolation,and extract the envelope frequency to determine whether the envelope frequency is the same as that of the TACAN baseband signal.If it is the same,combine the sorted TACAN reference pulses,it can be determined that the received signal contains the TACAN signal,and the effective reconnaissance of the TACAN signal is completed.In the azimuth calculation,this thesis uses the phase difference between the reference pulse and the zero-crossing point of the positive slope of the envelope to calculate.The position of the zero-crossing point of the positive slope is indirectly calculated by using the positional relationship between the zero-crossing point of the positive slope of the sine wave and the peak and trough of the wave.The phase difference is converted to the bearing of the TACAN signal.The simulation results show that the azimuth information in the TACAN signal can be calculated correctly. |
