Research And Realization Of Correlation Interferometer Fast Direction Finding Algorithm

The algorithm of interferometer as a fast algorithm of direction finding has been widely used in many kinds of direction finding systems, because of its advantages such as high speed, simplicity and high sensitivity. It includes phase interferometer and correlation interferometer. Phase interferometer is adopted in most shortwave broad band direction finding equipments since it could be actualized both easily and fast. However, it is sensitive to gain-phase error, and has poor anti-interference performance. The algorithm of correlation interferometer direction finding, which has the virtue of good anti-interference performance together with broad adaptability in different antenna array types, could overcome the problems in phase interferometer algorithm when using it in shortwave broad band direction finding systems. But due to the correlation interferometer' large computation real time processing is hardly realized if only use DSP. To solve the problem, a realization mode through making use of FPGA and DSP is brought in some project. According to requirement of the project, the algorithm of correlation interferometer is realized on the validation platform by this mode. The validation of algorithm and evaluation of resource are finished. This provides a foundation of this project. The main content is as follows:1. Studies phase interferometer and its relevant algorithm for solving ambiguity. Firstly, long-short baseline method, virtual baseline method and spatial baseline method which is commonly used phase algorithms of interferometer are studied in this paper. Then, because of the problems that arrays of long-short baseline method and virtual baseline method are limited, and that spatial baseline method has poor anti-noise performance, a new algorithm of solving ambiguity based on complex correlative computing is described. The emulation thows that this new ambiguity is suitable for many kinds of arrays and has better anti-noise performance than spatial baseline method.2. Researches algorithm of correlation interferometer direction finding. First of all, the principle of correlation interferometer is discussed in both time domain and spectrum domain. Secondly, in order to tackle the problem that correlation interferometer needs to consume a mass of chip resources when it is implemented on FPGA, this paper presents an improved algorithm, which is minimum distance method. And then the evaluation and comparison of resource consumption is presented when the two algorithms are carried out on FPGA. And the minimum distance method is proved that it can use lower resource and work faster by the results.3. Completes the design of correlation interferometer direction finding on the validation platform and actualizes it. First the shortwave broad band direction finding system is introduced, and the structure of the algorithm of correlation interferometer is designed. Second this paper presents the steps of implementing correlation interferometer, and analyzes the implement mode based on FPGA and DSP, achieves assignment allocation on FPGA and DSP, and detailedly introduces the function modules and design in internal FPGA. Last parameters of the direction finding system are listed, and performance of the direction finding system is tested. According to the results, the system could actualize real time direction finding for shortwave signals whose hopping rate is lower than 100, and bandwidth is lower than 500 kHz.