A Study On Passive Intermodulation Interference Of Base Station Antenna

The Base Station Antenna (BSA for short) is one of the important wireless equipments transmitting and receiving electromagnetic wave in modern communication system, especially in mobile communication network, also is an important part of wireless accessing system in mobile communication network. The Passive InterModulation (PIM for short) performance of it is very critical to the quality of whole network.The InterModulation products would be generated due to transmission of two or more carrier signal in communication system. Generally it is called PIM when the carriers transmit through passive components. The generation mechanism and mitigation measures of PIM are discussed within this paper. PIM interferences at microwave and RF frequencies are mainly originated from two types of passive nonlinearities, namely, contact non-linearity and material non-linearity. The former refers to any metallic contacts which have nonlinear current-voltage behavior. The later represents bulk materials which exhibit nonlinear current-voltage characteristics.This paper introduces the main construction of BSA first, and then the measurement of PIM is introduced, highlight the characteristics of the measurement of PIM on BSA. The main PIM interference sources on BSA are the metal screw connection between the radiation unit and reflector, the soldering on radiation unit, feeding network and DIN 7/16 connector input cable assembly which are verified by related test beds. Furthermore, other factors which will impact the PIM interference are the isolation parts and the way of BSA grounding.The PIM improvement are offered related to the main PIM interference sources, they are the metal screw connection replaced with the plastic insulation connection between the radiation unit and reflector, the improvement of soldering process on radiation unit, feeding network which are verified by related test beds. Furthermore, there is the improvement of connection between isolation parts and reflector. These improvements are critical to enhance the PIM performance of BSA, thereby improve the quality of connection and keep the design volume of system.