Astudy On Base Station Omni-directionalantennas For MIMO Communications

With the developing of communications and information technology, the number of mobile users is increasing gradually, while wireless communication resources may exceed the demand. IMT-Advanced system, which is based on the multiple-input multiple-output (MIMO) communication technology, is attracted much attention because of its features including fast transmission rate and high spectrum efficiency. As the conversion equipment for signals in wireless system, the study on the base station antenna is practically significant.Some base station Omni-directional antennas, satisfying the specifications of the system and working in four frequency bands are designed in this thesis. The printed dipole is adopted as radiation element and arranged in vertical and horizontal plane to construct an antenna array. The parallel double transmission line, printed on the both sides of the substrate is utilized as feed line, and a tapered transmission line is employed for impedance matching. After a detailed analysis of the impact of the structural parameters on the antenna, appropriate parameters are determined. The bow-tie antenna, with wideband properties due to the slow decay of the current, is employed to replace the rectangular dipole, for the coverage of two frequency bands and bandwidth extension.The equivalent circuit model of impedance is presented based on the transmission line model and circuit topology. A series circuit is equivalent to the designed series antenna array, and radiation impedance of each antenna is expressed as an impedance element in the circuit. The equivalent circuit model can be used for obtaining the array impedance if the coupling between the antenna elements can be accounted.The antenna arrays and the equivalent circuit model, proposed in this thesis can be employed as a feasibility basis for the antenna design and impedance matching.