Antenna Design And Performance Analysis Based On Fractal Structures

Antenna is an important part of communication system.In recent years,in various application fields,the volume of communication system and communication equipment is getting smaller,and the performance requirements are getting higher.This requires its internal antenna to operate normally at multiple frequencies while ensuring small size,and to have sufficient bandwidth and good gain performance.The electrical performance of an antenna is usually determined by its structure.It is easier to change or load the antenna structure than the parasitic element method.Fractal structure is a special geometric structure with self-similar characteristics and space filling.Its dimension is a fraction.With the development of fractal theory,some researchers have applied fractal structure to various fields and found that fractal structure has many excellent features.Many studies domestic and abroad have shown that the fractal antenna applied in the field of RF antenna has the advantages of multi-frequency operation and relatively large bandwidth under the condition that the size of fractal geometry is not increased,to some extent,it can solve the problems that traditional antennas had.In this thesis,based on the antenna theory,the design of fractal structure antenna,and then through numerical simulation analysis,the influence of fractal self-similar structure on antenna performance,and the relationship between the order of fractal and antenna performance.The Thesis mainly includes the following contents:1)Study the unipolar Sierpinski triangular fractal antenna.First of all,the order of the antenna is changed,and the relationship between the antenna size and the working frequency point is observed.Then,by changing the order of the antenna,the return loss curves of the second-order antenna and the third-order antenna are compared,and the surface current distribution is observed.The influence of the self-similar structure on the number of frequency points can be seen.2)A sinusoidal antenna with self-similar load factors from inner ring to outer ring is designed based on the theory of non-frequency-variable antenna.The inner diameter and outer diameter of the sinusoidal arm are determined by the preset working frequency range,and then simulated by simulation software.Observe the frequency variation of each electrical performance of the antenna,whether it meets the characteristics of non frequency variation.Then the terminal effect is reduced by loading the thread so that the reflected current at the end of the antenna arm approaches0.3)Combine the two fractals together to form a composite fractal antenna and adopt the indirect feeding mode of coupling feeding.The outer fractal can change the symmetry to affect the direction of current,and the inner fractal can broaden the bandwidth of working frequency points.By comparing different models and scanning optimization of antenna size,the performance will be better at some frequency points,and a reasonable structure can be selected to obtain a composite fractal antenna with multi-frequency operation.