Bandwidth Enhancement Of Dual-polarized Antennas Based On Upstanding Dipoles For Base Stations

Base-station antennas play a key role in mobile communication systems,which have direct and very important impact on the performance of mobile communication networks.With the rapid development of mobile communication technologies,2G/3G/4G/5G mobile communication systems have been deployed successively,covering the frequency bands of1710-2690 MHz,3300-5000 MHz,and 1427-1518 MHz for the international telecommunication communication system(IMT).Therefore,it is particularly important that the bandwidth of a base-station antenna can cover 1710-2690 MHz,3300-5000 MHz as well as 1427-1518 MHz simultaneously.The upstanding dipole antenna is a printed dipole antenna excited by a broadband balun,which features a simple structure,a light weight and ease fabrication.In this thesis,the bandwidth of a dual-polarized upstanding dipole antenna is enhanced to cover the frequency bands of 1.7-2.7 GHz,1.4-2.7 GHz,and 2.3-5 GHz,respectively.The main contributions of this work are summarized as follows.1.A broadband dual-polarized upstanding dipole antenna is developed to cover the frequency band of 1.7-2.7 GHz?The antenna feed structure and the length/width of the upstanding dipoles can be adjusted to fulfill the broad bandwidth.The shape of the broadband balun is modified to achieve better impedance matching.A metal rim is introduced to increase the antenna gain in the high frequency range and to reduce the cross-polarization in the low frequency range.Simulated and measured results show that the dual-polarized upstanding dipole antenna achieves a bandwidth of 45% for return loss >15 d B,covering the frequency band of 1.7-2.7 GHz with isolation > 30 d B,gain =about 8d Bi,and half-power beam width = 68°±5°.An 8-element antenna array is investigated,which demonstrates the potential applications of this antenna in 2G/3G/4G base stations.2.The bandwidth of the broadband upstanding dipole antenna is enhanced to cover the frequency band 1.4-2.7 GHz.A parasitic crossed metal strip is added to the above of the upstanding dipole for bandwidth enhancement.The metal crossed strip can not only enhance the frequency band but also improve the antenna gain.A metal rim is still used to stabilize the gain and reduce the cross-polarization.Simulated and measured results show that the bandwidth enhanced upstanding dipole antenna achieve a bandwidth of63.4%,covering the frequency band 1.4-2.7GHz with isolation > 30 d B,the gain =about8 d Bi,and the half-power beam = 68°±5°.An 8-element antenna array is also investigated,which shows the potential applications for this antenna in 2G/3G/4G and IMT base stations.3.One more parasitic crossed metal strip is added to the bandwidth enhanced upstanding dipole antenna for further bandwidth enhancement.A combination of two parasitic crossed strips can enhance the bandwidth to cover the frequency band 2.3-5 GHz.A metal rim is also needed to stabilize the antenna gain and reduce the cross-polarization.Simulated and measured results show that the further bandwidth enhanced upstanding dipole antenna achieves a bandwidth of about 75% with the isolation > about 30 d B,the gain = about 8 d Bi,and the half-power beam width = 68°±5°.A 3×3 antenna array is investigated.It found that the upstanding dipole antenna may be used in massive MIMO antennas for 4G and 5G mobile communication base stations.