Research On Wideband Dual-polarization Base Station Antenna And Passive Intermodulation Distortion In Antenna

In recent years, the third generation mobile communication technology has beendeveloped and commercialized. The fourth generation mobile communication technology isalso beginning to develop, therefore, several mobile communication systems will coexist inthe future. In order to save the installation resources for base station and reduce the cost ofnetwork construction, being compatible with a variety of communication systems at the sametime is required for mobile communication base station system. As the important interfacebetween electromagnetic wave and electric circuits, antennas have a direct impact on theentire communication system. So developing antennas which accommodate several wirelesscommunication systems with excellent electrical characteristics has important significance inadapting to different communication standards. So far, only a few antenna companies haveproducts which can meet the demand, and the key technologies are still grasped by foreigncompanies. As China involved in setting standards of the fourth generation mobilecommunication system, developing mobile base station antennas which have excellentperformance in wideband independently is of great significance.Modern communication systems require the improvement of spectrum utilization.Therefore, when similar frequencies exist in transmitting and receiving equipmentssimultaneously, interference in the system will increase. Passive Intermodulation is caused bya nonlinear device which is excited by high power. Passive intermodulation distortion maydegrade the performance of the multichannel wireless communication system. So research onPIM has become one of the key issues of the multichannel wireless communication system.First, a brief introduction to base station antennas technology and PassiveIntermodulation is given. Then a discussion to the current research status of wideband basestation antennas and Passive Intermodulation is conducted. In Chapter Two, the radiationprinciple of antenna，the basic parameters and the PIM problems in antennas are presented. Inthe third chapter, basic on complementary antennas, a wideband dual polarized radiatingelement for base station is presented. The proposed antenna can operate from1.71GHz to2.69GHz with VSWR<1.4and it has stable beam width and low back radiation. Then thechanges of the antenna radiation parameters affected by different sizes and shapes of the ground are discussed. After simulation and adjusted the structure parameters, an optimalstructure is found. Then the five elements antenna array, which used this radiating element, isstudied. In Chapter Four, the problems in testing such dual polarized base station antennas arediscussed, and the reasons why antenna radiation parameters change in traditionalmeasurements are also explained. In Chapter Five, the mechanism of Passive Intermodulationis analyzed and the measures for reducing PIM are discussed. Finally the effectiveness isvalidated through the experiments.