Design Of Several Fractal UWB And Multi-frequency Antennas

As the cornerstone of communication systems,antenna design has been one of the most important area of the communication researches.Ultra-wideband technology is a more mature and promising technology in the antenna design.The manufacturing cost of these types of antennas have huge savings compared to other types of antennas.There are other communication systems in the work band.This means the technology and other systems share the frequency band,which can effectively alleviate the lack of bandwidth resources.With the development of the antenna in the direction of multi-frequency and broadband,miniaturization and integration of technology have become hot spots.Fractal antenna can be regarded as a major application in the field of fractal,through the antenna structure of the regular iteration to produce a self-similar geometry which is independent of the scale of the antenna structure.With the change of communication technology,people’s demand for modern communication is also changing with each passing day.Modern terminal installation covered with different communication systems,which requires the terminal having multiple transceiver systems.A small terminal installation is difficult to have more than one transceiver antenna.The multi-frequency antenna that can operate in multiple frequency bands just solves this problem.Firstly,the background and research status of UWB,fractal and multi-frequency antennas are discussed.Then the development of these antennas are briefly introduced.The characteristics of UWB including ultra-wideband definition,standard requirements,advantages and disadvantages are discussed.The method of generating the notch characteristics of UWB antenna is discussed.Discussing the concepts and principles of fractal technology,especially the concept of dimension.Finally,the principle of multi-frequency antenna and related research techniques are analyzed.Three kinds of antenna based on fractal structure are introduced in detail.The tree structure is used as the basis of fractal iteration.These antennas all belongs to the UWB.The first part introduces a flower-shaped ultra-wideband antenna obtained by the fourth-order iteration and rotated from the basic tree element.Optimizing the iterative order,the number of unit groups and other key factors in the software so that the final formation of the antenna has a good impedance bandwidth and the size of the antenna significantly reduced.The second part is a slotted UWB antenna.The main part of the antenna is still based on the second-order fractal tree structure.The slotted floor is used to produce trap characteristics.The ring parasitic unit inside the fractal patch can achieve double trap function.The block band of this antenna correspond to the high frequency band of WLAN system.The third part is a single notched antenna.Gradient microstrip line is used as radiation patch feedline to improve the impedance match.By analyzing the characteristics of the order and groove shape of the fractal tree on the patch,the notched frequency band of the antenna corresponds to the WLAN band.Make these antennas,test them and give conclusions.This chapter describes several antennas used in WLAN and WiMAX systems in details.The first printed antenna used double ring structure and this structure can only achieve dual-frequency function.Adding a single branch can achieve tri-band function.The second antenna used an incomplete circular arc structure to form a double C-shaped printed antenna.The antenna has two operating frequency bands which can include WLAN and WiMAX band.Based on the shape of the second antenna,improving the structure of the antenna and joining the symmetry structure can achieve tri-band characteristics.These antennas are tested and they can cover the target requirements of the band.