Research And Implementation Of Shortwave Wideband DF Algorithm

With the development of shortwave communications, wideband signals including spread spectrum signal, frequency hopping signal and linear FM signal have been widely used in modern shortwave communication systems, which makes great demands on direction finding against burst and short-time signals. The shortwave wideband receiving DF technique has become the key point in the research area of shortwave DF. The traditional narrow band DF technique can't meet the requirements of wideband DF systems. This paper discusses how to estimate both DOA and spatial distribution of various signals in the wideband domain quickly and accurately and how to process mass data caused by wideband DF systems.At present, the widely used wideband DF technique at home and abroad includes the standard interferometer DF algorithm and the correlative interferometer DF one. The former has the merits of small calculating amount precise DF and the demerit of interferometer ambiguity-resolving errors to result in DF failure. The latter uses the correlation of raw sample data to avoid phase ambiguity and improve DF precision. In shortwave DF, the traditional correlative interferometer determines the azimuth and elevation angles of signals by searching the coherence crest value in all-aerospace and round-the-clock data. As to wideband DF, the correlative processing is computationally expensive on the basis of a mass of original data and usually uses the high-performance server or the embedded processor to form a platform for distribute processing, which is complicated, expensive and unable to meet the timeliness.This paper presents an improved correlative interferometer DF algorithm which introduces the concept of space angle to reduce raw sample data and lower computational complexity under the precondition of high accuracy of DF. Suitable for circular array and L-shape array, this algorithm is good for practical application in engineering for small computation, which shows it is a good method for implementation of phase ambiguity resolution of standard interferometers.Aimed at the application of wideband DF, the paper proposes a high-performance signal processing modular consisting of a multichannel AD and large-scale FPGAs. The paper uses FPGA for preprocessing of DF array signals and for correlative computation of all sub-channel, which makes the configuration of the wideband DF system simple, light, economic and reliable.