Researche On Broadband Base-Station Antenna

With the rapid development of mobile communication technology and the coming of 4G generation, now the mobile communication system is composed of 2G, 3G and 4G generation,which makes the communication system must have enough bandwidth to cover multiple systems simultaneously. The base station antenna is an important part of the mobile communication system, it will directly influences the performance of the mobile communication system, therefore, it is required that the base station antenna must has enough bandwidth, which will achieve a stability of Standing Wave Ratio, Radiation Pattern, Gain, Front to Back Ratio and Cross Polarization Ratio in a wide frequency band. Due to the complexity of the electromagnetic propagation environment, when designing the base station antenna, the dual polarization structure is usually adopted to obtain the diversity gain, which will counteract the effect of multipath fading and improve the quality of wireless communication. Due to the gain of an antenna unit is small, in order to improve the antenna gain, a plurality of antenna units can be combined together to form an antenna array, which will meet the Gain requirement of mobile communications. In addition, due to its suppression in rain and fog interference and multipath reflection advantage, the circularly polarized antenna has been widely used. In this paper, we have designed the dual polarization base station antenna unit and circular polarized antenna covering 690-960 MHz and 1.71-2.69 GHz bands. Summarized as follows:1, A broadband dual polarization base station antenna based on elliptical dipole is proposed, the antenna is composed of elliptical dipoles. The traditional straight dipole only have one mode, but when the dipole shape have changed into an ellipse shape, then there will be two modes, which will greatly increasing the bandwidth of the antenna. Test results show that the antenna meets a band range of 1.68-2.76 GHz for SWR<1.5, have a relative bandwidth of 48.6%, the antenna gain is about 8.23 d Bi, the antenna is suitable for mobile communication systems.2, Two broadband dual polarization base station antenna with T shaped feed structure have proposed, the radiation part and the feed part are all located on the surface of the FR4 substrate, the structure of the antenna is compact. Besides, the T shaped feed structure can effectively regulate the impedance matching of the antenna in a wide frequency band.3, Due to the coupling principle, a novel cross shaped dual polarization base station antenna structure with slot coupled feed structure is proposed. The antenna is composed of feeding part and radiating part, and there have gaps between the feed part and the radiating part, the overall structure of the antenna is like a figure ten. When different ports are excited, the current direction of the radiation section is perpendicular to each other. then it will achieve the dual polarization characteristics. On the basis of the structure, two kinds of base station antennas are designed: One is a dual polarization base station antenna based on PCB substrate structure, the other is a dual polarization base station antenna based on the structure of casting.4, Baed on the antenna structure in chapter three, two cross-shaped circular polarized antenna have proposed. This two antennas have the relative axial ratio bandwidth of 48.6%(1.85-2.72GHz) and 35.6%(670-960MHz),respectively.