Study Of The Transmitting Multi-beam Technique For Digital Array Radar

Digital phased array radar has been widely used in military and civil, because of its advantage, such as multiple working modes, multiple targets tracking and so on. Multi-beam technology is closely related to phased array. At present, receiving multi-beam technology has been mature, while transmitting multi-beam technology has been lack of research. This thesis is completed in digital array, based on the basic principle of the transmitter array. Depth study of the mechanism of the transmitting multi-beam in digital array, possible technical approaches and features, and engineering problems is done. This thesis also shows theoretical analyses and simulations, providing support for the engineering applications of the transmitting multi-beam simultaneously in digital array. The study is done from the following aspects:1. The development history of digital phased array radar is introduced. It also analyzes a comparison: the work mode of traditional phased array is time division, which is insufficient work for multi-objective; while the work mode of the transmitting multi-beam can work simultaneously not only in multiple airspace-ranges, but also in multiple working modes. From this comparison, the significance of digital transmitting multi-beam is found.2. Based on beamforming algorithm, three transmitting multi-beamforming algorithms are researched: transmitting multi-beamforming based on FFT、orthogonal projection algorithm and sub-array. According to the comparison of the algorithm analyses and simulations, it can be found that the algorithm based on orthogonal projection is more suited to the transmitting multi-beamforming simultaneously in digital array.3. With the implementation algorithm, there are some engineering problems. Some problems on implementation algorithm in transmitting multi-beam system are analyzed in this thesis, including amplitude and phase errors between channels, the position of the combination and weight, and the method of implementation algorithm, to provide a theoretical basis for solution to these engineering problems.4. As the main source of nonlinearity in transmitter, this thesis focuses on the influence of power amplifier(PA) nonlinear characteristics on the transmitting multi-beam. Firstly, a form of the multi-beamforming signal and a nonlinear model with memory for PA are given. Secondly, the output signal via the PA model has been analyzed. As the result of analysis, it can be found that the output signal is divided into the original signal and the interferential signal. The power ratio of original signal versus interference signal can reflect the influence of PA nonlinear characteristics on the digital multi-beamforming. Finally, the results of computer simulation show that in memoryless PA, the influence of PA nonlinearity on signal is related to the form of signal; in memory PA, the memory effect plays a key role for the small power signal, while the nonlinearity plays an important role for the large power signal. The conclusion provides a theoretical basis and reference to design PA.