Research On High Performance Printed Antenna Array For Mobile Communications

With the LTE commercially available around the world,2G,3G and4G mobilecommunication network will coexist in market to provide mobile services. Theantenna is the gateway of wireless communication networks. Since the new siteresources are becoming more difficult to obtain, using existing base-station site tosupport multi standard wireless network has become one of the main methods ofnetwork deployment. It’s very important to study base-station antennas which supportvarious communication networks with advantages of miniaturization, low profile andhigh performance.This thesis emphasises on the research and design of dual-polarized base-stationantennas applied to LTE,3G and some2G communication systems. The main andinnovative results are as follows:1. A printed dipole antenna element with a pair of short dipole patchs is proposedfor wideband applications. Two parasitic stubs are placed above the printed dipole,which are excited by the radiation field of the printed dipole arms. Experimentalresults show that an impedance bandwidth of80%for VSWR2.0, from1.54to3.64GHz, is achieved. Compared with traditional printed dipole antennas, the antennahas more than three resonant frequencies, and the relative bandwidth is almostdoubled.2. A printed dipole antenna element loading a pair of short "T"-shaped metallicstubs is presented. The "T"-shaped metallic stubs, which are symmetrically connectedto the two arms of the dipole, will work at the higher frequency, broadening thebandwidth of the printed dipole. There are total four antenna resonant frequencypoints. The proposed antenna exhibits an impedance bandwidth of80.5%forVSWR2.0, which means a onefold increase in bandwidth compared to traditionalprinted dipole antenna.3. The design and realization of a broadband dipole antenna with a new balun ispresented. An integrated balun with an branch strip is introduced as the feedingnetwork to enhance the antenna bandwidth, without changing the antenna size. A transmission line theory analysis method is presented for understanding themechanism of the wideband impedance matching. An antenna prototype is fabricatedand measured. The measured performances of the antenna show a good impedancebandwidth of58%for VSWR1.5.4. A wideband dual-polarized base station antenna composed of a pair ofdouble-layered printed dipoles with "T"-shaped patch loading is presented. Theantenna structure helps to enhancement the antenna bandwidth, suppress the crosspolarization level. A ladder-structure feeding balun is presented to improve isolation.The antenna achieves a common impedance bandwidth of66.7%(VSWR1.5) atboth input ports. The antenna has excellent performance in isolation, which is morethan25dB between the two input ports.5. A wideband dual-polarized base station antenna made out of a pair ofdouble-layered printed dipoles with branch-line feeding balun is presented. Theproposed antenna achieves a1.5:1standing wave ratio bandwidth of57.6%at bothports. The radiation patterns over the operating frequency band are stable.6. To meet the requirement of miniaturization and wide bandwidth for LTE basestation, an24array antenna is designed and fabricated. The antenna achieves acommon impedance bandwidth of1.8GHz-2.87GHz at both input ports of eachdual-polarized element, the experimental results show that the dual-polarized arrayantenna has excellent impedance matching performance.