The Research Of Shortwave Direction Finding And Location Technology

With the development of communication technology, the direction finding and location of the signals are more difficult for the third party due to wide use of network communication system, low probability of interception communication system, adaptive power control technology and adaptive frequency selection technique.The effective way of improving the ability of direction finding and location for short wave communication signals is to improve the timeliness of direction finding, use wideband channelized direction finding technology and construct wideband automatic crossing location system. This dissertation makes a research of method for shortwave narrowband direction finding system, wideband channelized direction finding system, and maneuvering direction-finding system. Furthermore, it analyzes the processing procedures of wideband networking location system, and proposes the improvement strategy and method. Finally it verifies the research result with the actual direction finding and location systems. The main contents and contributions are summarized as follows:1. For the fast computation of two dimensional spatial spectrum in circular array, this dissertation puts forward the fast methods for arbitrary circular array. First the structure of steering vectors of uniform circular array is analyzed. According to the special structure of steering vectors, the computation of spatial spectrum can be realized by fast convolution. Based on the thought of virtual array transformation, the arbitrary circular array can be transformed into virtual uniform circular array in which the element number is equal to spatial spectrum point. The fast computation of spatial spectrum can be realized by steering vectors of virtual circular array.2. To solve the fast computation problem of two dimensional spatial spectrum in arbitrary array, first the steering vector of array is divided into several steering vectors. And each deposed steering vector keeps correspondent with a certain virtual uniform circular array. This processing is equivalent to the fact that the original array is transformed into the array consisted of several virtual uniform circular subarrays. According to the fact that the number of effective phase modes is much less than the point number of spatial spectrum, the fast computation method for spatial spectrum using effective phase modes in mode space is proposed.3. For the computation complexity of channelized direction finding in shortwave wideband, the fast algorithm of correlative interferometer direction finder using guide baselines is proposed. The baselines can be classified into guide baselines and de-ambiguity baselines. Guide baselines determine the accuracy of direction finding and researching range of correlation degree while de-ambiguity baselines eliminate ambiguity results. And therefore, the accuracy of direction finding, processing timeliness and robustness of de-ambiguity are guaranteed. The dissertation deduces the expression of estimation error variance in any form of guide baselines and compares with Crammer-Rao bound. Furthermore, the dissertation takes the uniform circular array as a model, gives the measures of improving accuracy of direction finding, and proposes a rule to choose de-ambiguity baselines.4. Two amplitude-comparison direction finding methods are researched: Watson-Watt method and Wullenweber method. For the direction ambiguity and error calibration in Watson-Watt direction finding, this dissertation analyzes error model, gives the expression of direction finding error for amplitude and phase errors. Meanwhile it proposes a practical method of error calibration. For the problem of discontinuous amplitude in goniometer digitalization, the dissertation presents interpolation method for spatial sampling sequence to obtain the smooth effect.5. For the problem of signal sorting, parameter estimation, data transmission, and multi-station signal matching, the optimization of the procedures of crossing location is put forward. The dissertation researches the method of signal detection threshold and makes strategy of signal sorting. The amount of data transmission is decreased and the integrity of information is kept. Finally it proposes the method of multi-station signal matching to reduce ghost of location result.