A Study On Base Station Sector Antennas For Mimo Communications

IMT-Advanced communication system which is based on MIMO communication technology is attracted much attention because of its features including faster rate and higher spectrum efficiency. Therefore, as a key component of the communication system, base station antennas for IMT-Advanced frequency band, which is much important for the system implementation should be researched.A dual polarization sector antenna using microstrip patch as its element is adopted in this thesis. Microstrip Wilkinson power divider is chosen as the feed system and the desired requirements of characteristic parameters can be achieved through simulation results comparing with testing results.By means of broadband technology of symmetric dipole, bow-tie antenna has been selected as model of another base station sector antenna. The simulation results verify that the bow-tie antenna possessed a wider bandwidth than the microstrip patch antenna. Based on the principle that multiple resonances may achieve a wider impedance bandwidth, a new antenna structure named clover is proposed to broad the bandwidth furthermore. The cross polarization level is suppressed at the half-power beam width, which is superior to that of the bow-tie antenna.The low frequency characteristic can be improved if the antenna is slotted where the current magnitude is large. A new antenna model is proposed based on the principle and the wider frequency band than that of the clove antenna is achieved. It may work in three operation bands simultaneously. Therefore, fewer antennas are required and low cross polarization level is obtained. For the antenna feeding, two kinds of Wilkinson power divider are designed. By comparing the performances and fabrication complexities, one of the power divider is selected as the element of the antenna feed system. The selected power divider is relatively fabrication at the same performances of output port isolation and impedance bandwidth.The slotted clover base station sector antenna possesses the performances of multiband coverage, low cross polarization level and relatively simple structure. It is suitable for engineering applications.