Research On The Algorithms For Wideband Digital Beamforming

Digital beamforming, which has great significance of SNR enhancement, interference suppression, viability improvement, has a wide range of applications in radar system. After years of research, narrowband digital beamforming technology is very mature. However, with the development of electronic technology and the proposing of new requirements, wideband even ultra-wideband signal is used more and more widely in radar system, which leading narrowband beamforming algorithms cannot meet the needings. Research on wideband digital beamforming technology has made significant progress in recent years, but there is still much room for improvement in signal bandwidth, beam precision, implementation complexity, anti-interference ability and other aspects of the existing algorithms. Therefore, better wideband digital beamforming algorithms need to be further studied. In this paper, the following work on the problem of wideband digital beamforming in radar system has being done:1. Two frequency domain wideband adaptive beamforming algorithms, incoherent signal method(ISM) and coherent signal method(CSM), are studied. In this paper, it is pointed out that ISM algorithm cannot process coherent signal while CSM algorithm does by eliminating the singularity of coherent sources' covariance matrix with focusing transformation. Besides, three kinds of CSM altorithms, SST, RSS and LS, are discussed. And then, under different signal bandwidth and interference bandwidth conditions, ISM algorithms and these three CSM algorithms are use to wideband beamforming. The simulation results show they can achieve wideband beamforming, and have the ability of interference suppression.2. The conventional beamforming algorithm has poor performance when applied on wideband signal, for which one solution that adding time delay processing to this method is given. Delay accuracy largely determines the performance of wideband beam. In order to improve the accuracy, fractional delay filter which can achieve high-precision delay is used. Three kinds of fractional delay filters which based respectively on window function, farrow structure and hyperbolic structure are vestigated and used in wideband beamforming. The simulation results show that these three methods can achieve beam patterns which are close to the ideals. Besides, the last two methods have a great advantage that they can switch beam direction without changing filter coefficients.3. wideband transmitting multi-beam technology is vestigated. Each beam of parallel multi-beam algorithm is controllable independently and adjustable easily. However, this altorithm has a great consumption of resources. In this paper, fractional delay filter based on hyperbolic structure is used in the realization of a single beam,and then transmitting multi-beam is obtained with the parallel multi-beam altorithm. For the problem of resources consumption, two optimization methods are given. The first one is achieved by sharing parts of sub-filters between mulitple beams and the second one sharing the whole fractional delay filter. Finally, the simulation results are given, which demonstrate the feasibility of these two methods.