Miniaturization And Reconfigurability Of Antenna Design For Wireless Communication Systems

At present, with the development of wireless communication technology, wireless terminal products are required to the multi-functional and highly integrated, which leads the antennas of wireless terminal products to be miniaturization, broadband, high integration and high performance. With the development and promotion of the LTE standard, the LTE mobile phones will be popular and widely used, and the research of the LTE antenna will become a new hotspot. It is worth noting that the LTE mobile antennas should have wideband characteristics covering the working frequency bands of 2G, 3G and 4G, which will further increase the difficulty of cell phone antenna design. In addition, the demands for the communication capacity, communication speed and communication security are growing, but the electromagnetic spectrum is facing to a serious congestion and limitation. The utility of electromagnetic spectrum resource can be improved by using ultra wideband(UWB) antennas and frequency reconfigurable antennas. In the thesis, we study the designs of miniaturized antenna, multi-band antenna and ultra-wideband antenna with reconfigurable band-notch characteristics, which is for the demands and tendency of the modern wireless communication systems.Firstly, the thesis introduces the background of the LTE mobile phone antenna, ultra-wideband antenna with reconfigurable band-notched characteristics, which provides a basis for the design of antennas in the thesis. Simultaneously, two types of basic antennas(monopole and dipole) and their key parameters are briefly introduced as the theoretical basis of the thesis.Combining conventional forms of mobile phone antenna with LTE mobile phone antenna design methods, a small-size mobile phone antenna is presented in this thesis, which covers GSM850/900, DCS1800, PCS1900, UTMS2100 and 4G bands. It is fabricated by using a thin FR4 substrate, whose overall size is 9mm×35mm×3mm. The coupled-fed structure is used to improve the bandwidth of antenna, and the shorting strip, ground loop and lumped inductance are introduced to decrease the size of antenna. At the same time, the high efficiency and monopole-like radiation pattern of the proposed antenna can be obtained. The radiation efficiencies are up to 50% and 95% inlow-frequency band and high-frequency band, respectively. It should be pointed out thata 1-mm thick plastic casing with relative permittivity 3.0 and loss tangent 0.01 is usedin the simulation analogy to the practical circumstance. Finally, the prototype sampleantenna is fabricated and measured. The measured results are in good agreement withsimulated results.The thesis also analyzes a miniaturized UWB antenna fed by using CPW method. Gear-shaped structures are employed around the circular disc radiator to lengthen the electric current path for the miniaturization. The antenna exhibits well UWB performance, which is that the stable radiation pattern can be achieved within the operating frequency band and the fractional bandwidth of S11 less than-10 d B is more than 124% with respective to the center operating frequency of 8.2GHz. In order to mitigate the interference problem, it is necessary for UWB antennas to have intrinsic filtering properties such as IEEE 802.1a(5.15-5.35 GHz, 5.725-5.825GHz), HIPERLAN/2(5.15- 5.35 GHz, 5.47-5.725GHz), C-Band(3.7-4.2GHz), an arc-shaped slit is etched in the radiate patch and parasitic element added to background of radiation element in order to obtain single and double band-notched characteristics. The proposed antenna has good band-notched characteristics in different frequency band. Additionally, a UWB antenna with reconfigurable notched-band varying from 5 GHz- 6 GHz is proposed using in this thesis. By switching the state of the PIN diode, the electric current path of antenna can be changed. Therefore, the good frequency reconfigurable characteristic can be achieved.The proposed antenna has good performance of miniaturization, reconfigurability, multiband and wideband for wireless communication system, which provides a solid foundation for the potential applications and development of the next generation mobile communication system.