| Ultra-wideband(UWB)communication system has been developing rapidly in the field of wireless communication because of its high speed,low power consumption,low interference and high resolution.Meanwhile,the antenna as the transducing device to transmit and receive electromagnetic wave,is an important part of UWB communication system,which directly related to the performance of the whole UWB system.However,in the band of UWB,there are other narrow-band communication systems such as WiMAX and WLAN,which is difficult to avoid the mutual interference between UWB systems and these narrow band communication systems.Therefore,the research of UWB antenna with band-notched characteristics is particularly important.The radiation principle and analysis method of UWB antenna are studied,the basic properties and implementation of fractal are also studied.The study results show that the fractal's space filling can reduce the size of the antenna,and it's self-similarity can make the antenna realize multi frequency resonance characteristics.The antenna's bandwidth can be broadened after increasing the number of bands.It provides a theoretical for the design of the miniaturized UWB antenna.A tree fractal antenna based on rectangular structure is designed,and using the defected ground structure to improve the impedance matching characteristics between the frequency bands.Then,the antenna achieves the performance of covering the band of UWB.By increasing the number of iterations,the minimum working frequency of the antenna is reduced,and the miniaturization of the antenna is achieved.The size of the antenna is 27×22×1mm~3,and the antenna's working band covers 2.96-13.02GHz.In order to obtain better impedance matching characteristics in the whole band,the rectangular unit is changed into triangle.Then,the improved Sierpinski fractal UWB antenna is designed.The antenna achieves good impedance matching by using a coplanar waveguide feed structure and a trapezoidal structure ground.The antenna covers a band of3.1-10.6GHz.By increasing the number of iterations,the minimum working frequency of the antenna is reduced,and the miniaturization of the antenna is achieved.The antenna's size is 30×16×0.8mm~3,and it's radiation pattern has the omnidirectional radiation characteristics.The antenna's gain remains flat in the working band,and it has good radiation characteristics.In order to avoid the mutual interference between the UWB system and WLAN(5.15-5.85GHz)system.The front Sierpinski fractal UWB antenna is improved,and the?/4 open circuit stub is loaded on its radiation structure,the antenna achieves band-notched characteristic in the band of 5.10-5.90GHz.The results of the test show that the antenna produces notch band in 5.05GHz-6.05GH,which is basically consistent with the simulation,and meet the design aims.In order to further remove the mutual interference between UWB system and WiMAX(3.4-3.7GHz)system,the T shaped slot is etched on the Sierpinski fractal UWB antenna with single band-notched characteristic.Then,the antenna achieves dual-band notched characteristics in both WLAN and WiMAX bands.It is difficult to carry out test verification,because the width of the T shaped gap is too small to process.In addition,the tree-shaped fractal UWB antenna with dual band-notched characteristics is designed by etching two U shaped resonant slots.The antenna achieves dual band-notched characteristics in the WLAN and WiMAX bands.The test results show that the antenna can cover the band of 3.1-10.6GHz,and generate dual notched bands at 3.27-4.05GHz and 4.95-6.00GHz.The test is basically consistent with the simulation,which proves the effectiveness of the design. |
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