Dual-Polarized Antennas For Indoor Distributed Antenna Systems And Optimal Design Of Base-station Antennas

As one of the most important hardware equipment in mobile communication systems,the antenna has a great impact on the performance of mobile communication systems.With the upgrading of mobile communication technology,the performance of mobile communication system is getting better and better.But it also brings higher system complexity,requirements for the performance of the antenna on various aspects are also higher and higher.The antenna in mobile communication systems mainly include indoor distributed antennas and outdoor base station antennas.According to the actual demand of indoor distributed antenna systems,a dual-polarized omnidirectional antenna and a dual-polarized unidirectional antenna are designed.For outdoor base station antennas,a dual-polarized antenna element is designed first ly,then the shaped pattern of the base station antenna array with ten antenna elements is optimized by using the differential evolution algorithm.The main work of this thesis can be summarized as the following respects: 1.A compact broadband horizontally/vertically-polarized omnidirectional antenna with high isolations is presented for indoor distributed antenna systems(IDASs).The antenna is a combination of a horizontally-polarized(HP)element and a vertically-polarized(VP)element.Its HP and VP elements consist of four horizontal and vertical elliptical printed dipoles respectively.The HP and VP elements are connected by four broadside parallel strips(BPSs).The vertical dipoles locate between adjacent horizontal dipoles,which makes the antenna compact in structure.The dual-polarized antenna obtains a bandwidth of 45.5% from 1.7 to 2.7 GHz,and the port isolations are better tha n 30 d B without introducing large distance between vertical dipoles and horizontal dipoles.The HP and VP gains are higher than 1.7 d Bi and 2 d Bi respectively.For both horizontal and vertical elements,the radiation patterns in horizontal plane are omnidirectional with ripples less than 2.5 dB,and the cross-polarization levels are also below-25 dB in the horizontal plane.2.A broadband plus/minus 45 degree dual-polarized directional antenna is presented.The antenna is composed of two double unit and do uble folded dipoles,which leads to a wide bandwidth.Folded dipoles working at 1.7 to 2.6 GHz and 2.7 to 3.8 GHz are designed firstly,then a wideband double folded dipole covers 1.7 to 3.8 GHz is presented by connecting the two folded dipoles together.To get symmetrical radiation patterns,a double unit and double folded dipoles is proposed at last.A dual-polarized antenna is obtained by two perpendicular double unit and double folded dipoles.The dual-polarized antenna obtains a bandwidth of 76.3% from 1.7 to 3.8 GHz,and the port isolations are better than 30 dB in the whole frequency band.The antenna gains are higher than 8 dBi,and the cross-polarization ratios are larger than 20 dB.Simulated and measured results show good agreement across the entire frequency band.3.A plus/minus 45 degree dual-polarized antenna array with beam forming is proposed.The antenna element is composed of two loop-dipole antennas,a metal stent and a modified ground plane.A wide bandwidth is obtained by using loop-dipoles.To get stable radiation patterns in the horizontal plane,a modified ground plane with four vertical walls is applied.The dual-polarized antenna element obtains a bandwidth of 45.5% from 1.7 to 2.7 GHz,and the port isolations are better than 30 d B.The antenna gains are higher than 8 dBi.Stable radiation patterns in the horizontal plane with 3 d B beamwidths 65° ± 5° are also obtained.An antenna array with ten elements is optimized by the differential evolution algorithm for antenna beam forming.Through these designs,the antenna array obtains a gain of higher than 15 d Bi,the largest side lobe level in the upper half plane is lower than-20 dB,and the radiation levels in the lower half plane are larger than-12 dB,-15 dB and-18 dB for the first,second and third null points,respectively.