| Passive direction finding technology is widely used in electronic countermeasure,navigation, aviation and other fields because of its good concealment and high safety performance. Currently, the high resolution direction finding technique based on antenna array is a research hotspot. The MUSIC algorithm has a large amount of calculation and high requirement for the system hardware, so it has difficulty in engineering implementation.Although ESPRIT algorithm reduces the calculation,it has constraints on the shape of the array. So it is necessary to study a passive direction finding algorithm which has a small amount of calculation, a high real-time performance, a tolerance for the shape of array, and easy to project implementation.Different with active time reversal (TR) technology, virtual time reversal (VTR) technology does not send the received signals back to media space, but generates them using computer.This paper applies VTR technology to passive direction finding algorithm for communication station, that is, estimating the azimuth angle of source through scanning along the rectangular loop line on the plane xoy, the pitching angle through scanning along the rectangular loop line on the vertical plane, and the strict mathematical deduction of principle is presented. In addition,the passive direction finding system is built by System View software and the simulation experiments are carried out.In the passive direction finding system, the RF signal received by the cross antenna array is converted into an intermediate frequency signal after passing a bandlimited filter,then it is stored in order to estimate the DOA of source by the VTR algorithm and other algorithms.The designs and parameter selections of some key modules in this system, such as the bandlimited filter, anti-aliasing filter, A/D module and spectrum analysis module, are given in detail.When evaluating the direction finding precision of the algorithm, we adopt the Link-11 signal except the PSK signal, aiming to explore the performance of algorithm in the electronic warfare environment. In addition, simulation experiments are carried out respectively when the signal is in HF or UHF frequencies, and when the source is located in different locations.This paper uses some comparison algorithms such as the phase method, the MUSIC algorithm,the ESPRIT algorithm and the maximum likelihood algorithm. Moreover, we analyze the VTR algorithm for multiple incoherent sources as well as single source.The experimental results show that, the VTR direction finding algorithm has some characteristics: firstly,there is no limit to the geometry of antenna array,and it can be applied to array with any shape. Secondly, the amount of calculation is much smaller than the MUSIC algorithm, slightly larger than the ESPRIT algorithm, and has more advantages compared with the maximum likelihood algorithm. Thirdly, it has a similar direction-finding precision with the MUSIC algorithm and maximum likelihood, which is much higher than the phase method. Fourthly, the VTR direction finding algorithm needs to store the relative delays from each element to each scanning point in advance so that it can use them when estimating the DOA. So it requires more storage than maller than the phase method, the MUSIC algorithm,the ESPRIT algorithm and the maximum likelihood algorithm, which means the VTR algorithm obtains a fewer running time through a larger storage room. Finally, the VTR direction finding algorithm is not effective under any circumstances. When ?s <45°.the azimuth estimation value (?)_s s has a large deviation, which is not credible, therefore when using the algorithm to estimate the DOA of source, we must pay attention to the scope of application. |
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