Aperture-shared Dual-broadband Antennas Based On Upstanding Dipoles For Base Stations

In mobile communication systems,base-station antennas play critical roles since they are directly related to the performance of the entire communication systems.With the continuous development of mobile communication technologies,2G,3G,4G,and 5G systems have been widely developed.The requirements for base-station antennas are also increasing.For coexistence of 2G/3G/4G/5G mobile communication networks,base-station antennas are required to cover the frequency bands for multiple communication systems.The miniaturization and/or the low profile of base-station antennas are also needed for modern base stations.In the future,multiple mobile communication systems must coexist with multiply frequency bands,for example,690-960 MHz and 1710-2700 MHz for China's 2G/3G/4G systems cover and 3.3-3.6 GHz and 4.8-5 GHz for 5G systems.Usually,it is difficult to cover such a wide bandwidth for a single base-station antenna.In this dissertation,aperture-shared dual-broad antennas are investigated based on upstanding dipoles since they have a minimized cross-section.The main contributions of this work of are summarized as follows:1.An apertured-shared dual-broadband antenna is developed for base stations based on upstanding dipoles using vertical chokes.The dual-broadband aperture-shared antenna consists of a low-band antenna and four high-band antennas.The low-and high-band antennas are all dual-polarized with upstanding dipoles fed by a broadband balun and share the same reflector or the same antenna radiation aperture.When the same polarization port of a high-band antenna is excited,a coupling current will be generated on the low-band antenna.As a result,electromagnetic waves will radiate from the low-band antenna,which will interfere with the radiation of the high-band antenna,causing pattern distortion and impedance mismatching in the high-band.Vertical chokes are introduced to the low-band antenna to reduce the scattering of high-band electromagnetic waves.When the lowfrequency antenna is excited,a common-mode coupling current will be generated on the high-frequency antenna.When it radiates,it will affect the radiation pattern at some frequencies on the low-band antenna,making its beam wider and gain lower.A rectangular slot is introduced on the ground plane of each broadband balun and extended reversely to the ground structure,so that the radiation of the induced current will be shifted from the low-band.Simulation and measurement results show that the aperture-shared dualbroadband antenna covers 690-960 MHz and 1700-2700 MHz(|S11|<-14 d B)with 7-d Bi gain in the low-band and 10-d Bi gain in the high-band for two elements.2.Horizontal chokes are introduced to the aperture-shared dual-broadband antenna for a lower antenna profile.The dual-broadband antenna is composed of a low-band antenna and four high-band antennas.The horizontal choke is a pair of arc-shaped metal patches connected by metal strips,which can more effectively suppress the radiation of the induced current on the low-band antenna,and can well adjust the impedance matching of the lowband antenna to cover 0.69-0.96 GHz.For the common-mode induced current on the highband antenna,a rectangular slot and an extended anti-phase grounding structure are still adopted on the high-band balun.Simulation and experimental results show that the horizontal chokes can make the low-band antenna impedance matching easier.The dualband antenna can cover 690-960 MHz and 1700-2700 MHz(|S11|<-14 d B)with 8-d Bi gain for the low-band antenna and 10-d Bi gain for the two-element high-band antenna.3.An aperture-shared dual-broadband antenna is investigated with bandwidth enhanced high-band antennas.The dual-band antenna is composed of a low-band antenna and four high-band antennas with enhanced bandwidth of 1.4-2.7 GHz.A new choke is designed on the low-band antenna to suppress the coupling introduced by the broadband high-band antennas.Due to the increased height of the high-band antennas,the side length of the coupled low-band current path causes the maximum coupling to a lower frequency.Therefore,it is only necessary to extend the reversed grounding structure on the high-band antenna balun.Simulation results show that the dual-band antenna can cover 690-960 MHz and 1400-2700 MHz for |S11|<-14 d B.The aperture-shared dual-broadband antennas based on upstanding dipoles have simple structures and are ease for fabrication,thus may find wide applications in 2G/3G/4G/ or even 5G base stations.