Study On The Radiation Control Mechanism And Signal Processing Of Space-Time Four Dimensional Antenna Arrays

Antenna Array is an important part of modern wireless electronic system.It is the key technology in wireless communication and radar which plays a decisive role in the overall performance of a system.It is the only way for the development of wireless electronic system in the new era to start from the physical essence of electromagnetic wave propagation and from the radiation control mechanism and signal processing of a novel array antenna.Fortunately,the space-time four-dimensional antenna array studied in this dissertation is a new type of antenna array which is introduced "time" into the traditional antenna array as the fourth degree of freedom.On the one hand,it can carry out time modulation through RF switch devices to realize the precise equivalent amplitude weighting of the antenna array elements at the center frequency and the precise equivalent amplitude and phase weighting of the sidebands,so as to achieve precise control of the radiation pattern of the antenna array.The use of "time" as a degree of freedom not only increases the design flexibility,but also significantly improves the radiation control ability and greatly simplifies the design of the feed network.On the other hand,compared with the traditional antenna array,the signal transmitted by four-dimensional antenna array is time modulated.Thus the unique property of time modulated signal is called direction modulation characteristics which means the transmitted waveform in different directions differ from each other.Using this property,the 4-D antenna array is with a great application prospect in a new generation of wireless communication system especially secure communication and RF stealth.The works of this dissertation focus on the research of the mechanism of radiation of the 4-D antenna arrays,in order to answer some specific questions still existing in the theory and principle verification.This work is also devoted to deal with the radiation challenges arised by “time”.Moreover,the author also try to analyze some system level challenges which hindered the practical process of the 4-D antenna arrays while “time” may bring infinite possibility in inproving radiation performance for the design of the wireless electronic systems.Finally,the author strive to narrow the gap between basic research and system application,and analyze a series of system compatibility issues.This dissertation constructs a theoretical model with time modulated signal at first.Then a novel RF switch devices work mode namely,multiple time frequency modulation,to suppress the peak sideband level is proposed.Moreover,the optimization algorithm which improves the optimization efficiency as well as further reduces the sideband energy loss is introduced.Effects of time modulation of the 4-D antenna array in signal transmission is then analyzed and the characteristics of the 4-D antenna arrays to transmit chirp signal is provided which will offer theoretical support for the research of wireless electronic system in the future.It should be noticed that a high performance test platform for the measurement of four-dimensional antenna array radiation pattern is built.The main innovations of this paper are summarized as follows:1.For the first time,based on the physical essence of sideband formation,a 4-D antenna array peak sideband level suppression method based on multi time modulation frequency is proposed.Then the radiation pattern of 4-D antenna array is deeply analyzed.The method proposed in this work is more flexible.When the proposed method is utilized the same low sidelobe pattern at the center frequency will be generated and the sideband level can be minimized as well as the energy of the sideband is the least.This work can help researchers to understand the mechanism of the time modulated radiation and the efficient optimization design of the radiation pattern for a 4-D antenna array.2.The distortion of the transmission signal of a 4-D antenna array is formulated.For the first time,the LFM signal is introduced into the 4-D antenna array and the distortion of the signal in all directions is analyzed under different control sequence.The relationship between bandwidth and time width of transmitted signal,time modulation frequency and control time sequence is clarified.This work can help researchers to understand the signal transmission characteristics and objective analysis of 4-D antenna array in the application of wireless electronic system.3.Experiments verify the directional modulation technology of 4-D antenna arrays.Based on improved genetic algorithm,a squential optimization control algorithm is then proposed.It is designed to optimize the graph of fidelity factor in physical layer secure communication.This work enhances the reconfigurable ability of signal transmitted by 4-D antenna array without distortion the range of the expected angle while distorted in the non expected range.This technology has great application value in the application of secure communication and radio frequency stealth system.This dissertation is to integrate the radiation pattern and the theoretical model of the signal transmitted by 4-D antenna array.Then this research work makes it clear how to control the radiation characteristic with “time”.Furthermore the coordination of signal processing method and system design of wireless electronic system is improved.Finally the ability of overall system performance can be promoted by 4-D antenna array.