Research On The Key Technology Of Transmitting Null Beamforming In The Low Intercept Communication

The null beamforming technology is an important aspect in the study of digital beamforming(DBF). However, the null beamforming technology is usually used in receiving mode and the study on transmitting mode is relatively less. In fact, the transmitting null beamforming technology also has a wide range of applications, such as improving the ability of anti-interference and anti-reconnaissance to satellites, jammer, and reconnaissance aircraft, improving the ability of anti-radiation missile attack, avoiding the active interference of allied radar and other detection equipment. These applications make the transmitting null beamforming technology attract more and more attention. The transmitting null beamforming technology in this dissertation, mainly focus on eliminating the interception and detection of the jammer or reconnaissance aircraft and other reconnaissance equipment to the transmit signals, realizing the low intercept communication. The study of this dissertation is done from the following aspects:1. The transmit model of array signals is given out and the basic knowledge of transmitting beamforming is introduced. The orthogonal projection and Capon classical transmitting null beamforming algorithms are studied. Finally, the simulation experiment of the two algorithms is performed.2. The method of null broadening of the transmitting beamforming is studied for the situation that the null direction cannot be aligned. Two classical algorithms, the Capon and the method of the derivative constraint are presented and compared. The analysis results show that these algorithms have large computation and little flexibility. Therefore, the research of null broadening for several common beamforming algorithms expanded is done. It is easy to find that null broadening algorithm improved orthogonal projection has less calculation and can quickly and flexibly realize null broadening for transmitting beamforming.3. In view of the radar system may have amplitude and phase error and other factors, based on Capon and LCMP null broadening of transmitting beamforming algorithms, some robust techniques are studied. By using the norm constraint and robust beam shaping method, the sensitivity of transmitting beamforming algorithm against amplitude and phase error is able to be reduced and the robustness of the algorithm is maintained.4. For the situation of transmitting broadband signal, the broadband signal array model is established and the basic knowledge of wideband trantmitting beamforming is introduced. Then from two aspects, frequency domain processing and time domain processing, the wideband frequency domain transmitting null beamforming algorithm and the transmitting null beamforming algorithm based on TDL structure are studied. The performance and the simulation of these algorithms are analyzed. At last, by combining narrowband weight with time varying wideband weight, the wideband null broadening of transmitting beamforming is realized and the simulation experiments are given out.