Research On Multi-frequency And Wideband Antenna Technology Based On Fractal Structure

With the rapid development of modern communication system,the antenna used for information transmission and reception has been widely used.The massive application of antennas has made the requirements on antenna performance more stringent.The antenna has a wider working frequency band and can work in multiple frequency bands at the same time.It has become an important goal of antenna design to have smaller size,better radiation characteristics and radiation gain.Therefore,it is of great significance to the research and development of miniaturized,multi-frequency and wideband antennas with high gain.Through a lot of research on the characteristics and performance of fractal antenna,the fractal structure is introduced into the antenna design in the field of electromagnetic theory,which can make the antenna have better miniaturization,broadband or multi band characteristics.Therefore,fractal structure plays an important role in the field of antenna design and has become an important research hotspot in the field of antenna design engineering.Based on the fractal structure theory,this paper studies the multi-frequency and wideband characteristics of fractal antennas.The paper's work as follows:(1)The basic theory of fractal structure and the basic properties of fractal structure as well as the implementation methods are discussed.The results show that fractal can reduce the size of antenna structure and generate multiple resonance points to generate multi-frequency and broadband characteristics due to the spatial filling and self-similarity obtained by the iteration of structure,forming the theoretical support for the design of small fractal antenna in the following chapters.(2)A design method of fractal dipole patch antenna based on binary tree fractal structure is proposed.The antenna is fed by the microstrip line after the impedance transformation.The parallel double-line structure and U-groove technology are adopted to optimize the impedance matching and reduce the resonant frequency of the antenna.The miniaturization was realized by using fractal technology.After a lot of simulation analysis,the final size was optimized to be 35 mm × 22 mm ×1.6mm,and the frequency band was 2.77-2.97 GHz.And using the above binary tree-like fractal structure as the array element,an array antenna with multi-frequency characteristics is designed.The array adopts a linear array structure and by adjusting the number and spacing of the array elements,a peak gain of 9.8 d B is realized.There are five working frequency bands,and the working frequency band of the array antenna at low frequency has a large bandwidth and good gain.(3)In order to meet the needs of modern broadband communication system,the fractal broadband antenna is studied.Based on Sierpinski fractal theory,an improved hexagonal fractal broadband antenna applied to L-band,S-band and C-band is improved.The antenna is fed by microstrip feeding technology.The final size of the antenna is 36 mm × 28 mm × 1.6mm,the operating frequency band is 1.10-7.76 GHz,and the maximum gain is 10.83 d B.In addition,the Sierpinski structure is used as a basis for improvement,and a type of Sierpinski fractal antenna design method is proposed.The radiation patch is a "mi" shaped fractal structure similar to Sierpinski fractal.The ground floor on the back of the dielectric substrate is sloted to improve the frequency,suppress the harmonics and expand the bandwidth.The final size of the antenna is 21 mm × 36 mm × 0.5 mm,and the operating frequency band is 1.64-5.57 GHz.(4)An ultra-wideband fractal antenna is designed based on Koch fractal,and a ground plate with defective structure is designed to improve the impedance matching characteristics and broaden the working frequency band.Through fractal iteration,the resonant point of the antenna is increased,the working frequency band is broadened,and the miniaturization is realized.The working frequency band of the antenna is 2.93-11.01 GHz,covering the whole UWB band.The final size is15 mm × 20 mm × 1.6 mm,and has good radiation characteristics.