| With the rapid development of wireless communication technology,the antenna as one of the key devices of radar and communication systems,its performance plays a decisive role in the communication quality or detection capability of the whole wireless system.Therefore,with the increasing number of modern communication services,research into the design of miniaturized,multi-band,wide-band,high-gain,and well-radiated antennas has become the main objective of current and future antenna design.The introduction of fractal technology can solve the problems in the traditional antenna design,its own self-similarity provides a new research idea for multiband resonance to further be able to extend the bandwidth,while another space-filling characteristic can effectively increase the space utilization of the antenna and realize the miniaturization of the antenna.Thus,antennas designed with fractal structures have gradually become an important research hotspot in the field of antennas and have good application prospects.In this paper,starting from the theory of fractal technology,the research is carried out from several different angles to realize the miniaturization,multi-frequency,and broadband characteristics of fractal antennas as well as to improve the anti-interference capability of antennas,as follows:(1)Design and study of fractal multiband and broadband antennas.Firstly,a fractal ring broadband antenna with gradual width is designed,by using the characteristics of the fractal ring,the antenna can work in S,C,X,Ku,and part of the K-band simultaneously,while using Defective Ground Structure(DGS)as the grounding plate and fed by microstrip line through impedance transformation,which further improves the impedance matching of the antenna,and extends the bandwidth to 2.63-20GHz with peak gain up to 9.8dBi.The measured and simulated results of the antenna are in good agreement with each other,which proves its effectiveness and application value.Secondly,a circular fractal antenna for broadband wireless communication is designed.By using circular and square iterative nested fractal structure as the radiation patch and analyzing the effect of different iterations on the antenna performance,the antenna can operate in five frequency bands where the return loss is less than-l0dB,i.e.,including IEEE standard wireless band,ultra-wideband range,X-band,Ku-band and K-band,Ku-band,and K-band,achieving multi-frequency characteristics.The antenna has a relative bandwidth of up to 162.3%(2.9128GHz)and a peak gain of 7.9dBi,and the radiation performance of the antenna is relatively similar and stable in each frequency band.(2)To meet the requirements of broadband communication systems,a fractal ultra-wideband antenna is further investigated.An ortho-pentagonal fractal ultra-wideband antenna has been designed using a fractal structure with iterative nesting of ortho-pentagonal and circular shapes as the radiating patch,a fractal orthogonal ultra-wideband antenna is designed,which is only 20mm×16mm×1.6mm in size to achieve the purpose of miniaturization,and the impedance matching of the antenna is optimized by designing the symmetrical slotted both sides of the decutting ground plate,and the ultra-wideband characteristic of 3.1-12.2GHz is achieved with the maximum gain of up to 5.26dBi,enabling stable omnidirectional radiation.Based on the same iterative approach,a compact hexagonal-triangular fractal ultra-wideband antenna is designed,which achieves ultra-wideband characteristics from 3.1-18.82GHz with a hexagonal connection through triangles,and also covers the whole Ku-band with a maximum gain of 7.8dBi,and can radiate electromagnetic waves stably,which can be used as a reference for future research and practice of ultra-wideband antenna design.(3)To improve the anti-jamming capability of the antenna and at the same time reduce the waste of spectrum resources,A Sierpinski-like fractal ultra-wideband antenna with triple bandnotch characteristics is designed.The main radiating patch of the antenna is a square hexagonal shape,and each order of the fractal structure is composed of four crescent slits of equal size to achieve the ultra-wideband characteristics from 3.1 to 18.0GHz.By etching the notch structure at three different locations,interference from the international satellite band,WLAN band,and the international telecommunication union(ITU)band is effectively suppressed.In addition to the notch band,the antenna also has good omnidirectional radiation characteristics and stable gain,which can be widely used in various ultra-wideband systems.In this paper,different types of fractal antennas are designed based on a fractal structure with a certain application value,which provides reference ideas for the future design of broadband,multi-band,miniaturized,and multi-band notch function antennas. |
