| As people's demand for the bandwidth in the field of wireless communications becomes larger,the original narrowband communication system has been unable to meet the people's increasing demand.In order to solve this problem,ultra-wideband(UWB)technology was invented at the historic moment.At first,the ultra-wideband technology was mainly used in the field of national defense and military fields.The communication system of military can effectively reduce the number of communication antennas,reduce the interference between the antennas,enhance the security of the communication process and enhance the concealment and mobility of military equipment by using this technology.With UWB officially open for civil use,by compared with traditional wireless communication technology,the antenna has the advantages of small volume,covering a wide range of frequencies and high safety features to get the attention of the people.Variety of civilian equipment who used the UWB technology was quickly invented.At the same time,the update speed is very fast.In the UWB technology,the design of wideband antenna is one of the most important technologies.So it is very important for improvement of the UWB technology and people's living standard.The difficult point of design ultra wideband antenna is for ensuring the communication signal in the specified frequency band low distortion.The antenna must continue to optimize the physical parameters to obtain good radiation characteristics.At the same time,for the sake of increasing the impedance bandwidth of the antenna,the antenna need to be optimized by using various of frequency band expansion techniques.From several kinds of antennas' structure,the microstrip antenna who has the advantages of small volume? easy manufacture and easy integration was chosen.After that,several design methods of wideband microstrip antenna were described and some target parameters of an UWB antennas were proposed.Based on this design methods,two different designs are presented.The feasibility of the design method was verified by an example.It discussed in detail the design method of microstrip antenna who has the advantages of small volume? easy manufacture and easy integration.It described several kinds of these antennas' structure and design method,at the same time to put forward the target parameters.It puts forward two different UWB antenna design by the design method of learned,and the feasibility is verified by examples.A wideband planar monopole antenna which use microstrip fed was designed by using the traditional microstrip antenna design method.In order to expand the impedance bandwidth,the defect ground structure(DGS)is used.The influence of DGS parameters on the antenna performance was emphatically analyzed.The test results show that,after used DSG,the upper limit frequency of this antenna was increased.The center frequency of this antenna is 9.5GHz,the input impedance bandwidth is 12.8GHz(3.1-15.9GHz),and the relative bandwidth is 133.7%.An wideband tree-shape antenna is proposed by using the fractal theory.This antenna fully embodied the advantages of fractal structure.By using characteristics of self-adaption and space-filling to attain impedance matching,the antenna performance was improved and the size of the antenna was effectively reduced at the same time.Through optimization,the fractal antenna's center frequency was 10.93GHz? input impedance bandwidth was 13.54GHz(4.16-17.7GHz)and relative bandwidth was 123.9%. |
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