Researches And Design On Wideband Base Station Antennas

With the rapidly development of mobile communication technology in recent years,the coexistence of 2G/3G/4G/5G communication systems has been formed.In order to reduce the laying quantity of base station antennas for saving coast and installation space,wideband basestation antennas are urgent needed.For different application equirements of communication,the type of antenna needs to be selected reasonably.As for conventional base station,the communicationa area can be covered by three directional antennas with horizontal 3-d B beamwidth of around 65°.However,there is not enough space to set up three directional basestation antennas for special micro base station,omnidirectional base-station antennas can be selected to realize 360° uniform radiation.To fit different communication scenarios,the design methods of directional and omnidirectional antennas are reaserched.Two types of dualpolarized directional base-station antennas and horizontally polarized omnidirectional antennas are proposed in this thesis.The main contents of thesis are as follows:(1)A wideband dual-polarized crossed-dipole base-station antenna in 1.42-2.83 GHz frequency band is proposed.It includes a pair of cross-dipoles,a pair of broadband baluns and a shaped metallic reflector.The crossed-dipoles are fed by the baluns to realize duai-polarized radiation.To wide the bandwidth of the proposed antenna,the tapered integrated baluns are employed.The reflector with shaped sidewall is designed to stabilize the 3-d B beamwidth in the horizontal plane at 66.3o±2.8o within the frequency band.(2)A wideband dual-polarized foled dipole base-station antenna in 1.42-2.83 GHz frequency band is proposed.Each antenna element consists of four folded dipoles,a parasitic patch,a pair of feed baluns,and a reflector.The folded dipoles are fed by two feeding baluns to realize dual-polarized radiation.To improve the impedance matching,the feeding baluns is designed with tapered structure.To further improve the impedance bandwidth and stable the radiation pattern,the parasitic patch is designed directly above the radiator.Based on the antenna element,a four-element antenna array with 3-d B beamwidth in the horizontal plane of 65°±5° is presented.(3)A compact horizontal polarized ominidirectional base-station antenna in 2.3-3.9 GHz frequency band is proposed.To achieve omnidirectional radiation of horizontal polarization,three curved dipoles are printed around a dielectric cylindrical shell of compact size and fed by the feeding network.To reduce the gain variation to 1.2 d B and improve the impedance matching of the proposed antenna,the directors are employed above the dipoles.A 1-to-3power divider and three baluns are used to design the feeding network without increasing the overall dimension of the antenna.Base on this design,a compact antenna with total volume of0.18? × 0.18? × 0.18? can be get(? represents the wavelength of the lowest operating frequency).(4)A wideband horizontal polarized ominidirectional base-station antenna in 2.3-3.9 GHz frequency band is proposed.To realize horizontally polarized omnidirectional radiation,four curved dipoles are printed on a dielectric cylindrical shell in a compact size.Four parasitic strips are embedded between the dipoles to decrease the gain variation and enhance the impedance.A 35 ? coaxial cable serving as a quarter-wavelength impedance transformer is used to design the feeding network without increasing the overall dimension of the antenna.Measured results show that the gain variation in the operating band is less than 1.6 dB.