Designs Of Ultra-Wideband Antennas With Fractal Structure

The Federal Commission(FCC) authorized the 3.1- 10.6GHz in 2002 as civilian and commercial communication frequency band. Antenna as one key device of the most important components in wireless communication systems, which performance directly determines the quality of the whole system. There are other narrow band communication systems in the standard 3.1- 10.6GHz system of UWB band like wireless local area networks(5.2- 5.8GHz) and Worldwide Interoperability for Microwave Access(3.3-3.7GHz), while UWB system works with those narrow band systems. It is necessary to eliminate the interference, so UWB antenna with multiple band-notch is proposed.In this letter novel printing UWB fractal antennas and with multiple band-notched using EBG structure are analyzed, optimized and measured. The main chapter is as follows:In the third chapter and fourth chapter, two small novel UWB antennas are proposed in order to meet the requirements such as miniaturization, low cost, easy integration and so on.The first antenna is compact fractal structure. It is found that by addition of eight tiny fractal elements at the corner of a polygon patch,standard UWB bandwidth can be corver while antenna dimensions are only 28×25mm2. Its structure is similar to the Koch curve and achieve a super wide bandwidth from 2.8 to 15.1 GHz. The second design is an iterative fractal antenna.The proposed antenna has total size of 30×30mm2 and can be used for 3.1GHz—14.3GHz frequency range. Experimental results show that these two characteristics of good resonance frequency, bandwidth to meet the requirements and H patterns approximately omnidirectional radiation.Based on the previous two chapters, the chapter 5 solve the potential interference problem in the ultra—wideband, and the MT-EBG structure is designed to have a very good notch function. Firstly, we prove that the MT-EBG structure can be used to implement the stop band characteristics. In order to design 5.0GHz-5.8GHz notch band, we only use one EBG structure, and then using of two EBG structure to achieve two suppressed frequency band:the 3.3GHz- 3.7GHz and 5.0GHz- 5.8GHz. In this chapter, the effect of EBG structure size on the performance of the stop band and the coupling problem of MT-EBG structure are also studied, which prove the effectiveness and simplicity of the MT-EBG structure. These two antennas has very good suppression function, and the notch frequency can be adjusted alone without interference.According to the result of simulation analysis and optimization, the antennas are processed and measured. The testing resulst of antenna are highly close to the simulation results.Those antennas can be used to the Ultra—wideband wireless communication systems.