Research And Implementation Of Wideband Coherent Source Direction Finding

Electromagnetic environment is becoming more and more complex in modern wireless communication; the density of communication signals which locate in a common band is higher and higher. A lot of signals with the same frequency or coherent sources appear at one time. Detection equipments available face more and more troubles, for instance, detection of multiple signals which are coherent or have common frequency, high resolution direction finding of wideband sources, weak signal extraction, multi-target signals tracting, are all great difficult problems. At the present time, classical spatial spectrum estimation algorithm can not process wideband coherent sources. Consequently, it is meaningful to study precise direction finding techniques of broadband coherent sources.Broadband coherent sources spatial spectrum estimate algorithms are investigated extensively in the thesis. Mathematic model of wideband coherent source is built, by which we study characters of broadband coherent sources and its effect on spatial spectrum estimate algorithms.Considering coherent signal subspace algorithms have the drawback that it needs the pre-estimation of DOA. Coherent signal subspace algorithms which based on scanning angle are proposed. Through forming orthogonal projection operator, the information from scanning azimuths reserved, while information from other azimuths is suppressed. So the new method achieved good performance with no need of pre-estimation of DOA. Compared with other methods, the algorithm can achieve perfect performance when center frequencies of the wideband sources are not the same. When signal subspace estimation is not perfect in the reference frequency bin, the spatial spectrum estimation would be seriously distorted in the test of orthogonality of projected subspace (TOPS). To resolve the problem, the paper proposed a MTOPS algorithm, which enhances the algorithm's robustness and provides the ability of decorrelation through conjugated reconstruction of the array covariance matrix.High order array cumulant has abilities of extending aperture of the array and suppressing noise (including Gaussian noise and non-Gaussian noise). Utilizing signal subspace focusing algorithm, we proposed wideband spatial spectrum estimation method based on high order cumulant, which can reduce the effect of noise on spatial spectrum estimation, the precision of direction finding is improved effectively.ESPRIT needs the shift-invariance property of the array, this thesis proposed a ESPRIT wideband direction finding algorithm based on high order cumulant. Using virtual element of array in high order cumulant, we break through the limitations of ESPRIT to array. The algorithm is applied to circular array which dose not have shift-invariance property successfully.Finally wideband signal direction finding engineering implementation techniques is studied in detail. Considering the characters of broadband signal processing, realization of the algorithms is analyzed. We discuss system composition, operation principle, hardware design, software design and technical specifications, determine working flow of direction finding, and form a reasonable division of hardware realization of functions. To reduce time of operation, the spatial spectrum estimation algorithm is optimized. Results of performance test in outdoor test site is given, comparison between actual direction finding results and that of simulations is drew, by which the efficiency of the direction system is shown.