Study On Broadband,Multi-band And Beamforming Techniques For Mobile Communication Antennas

The rapid development of science and technology has greatly promoted the progress of mobile communication systems.To provide better wireless communication services,several mobile communication systems have been designed and widely commercial used.So the coexistence and advancement of multiple mobile communication systems,such as 2G,3G,4G,WLAN and so on,have become the current situation and future development trend.Based on the large-scale application of 4G communication systems,research of 5G mobile communications has already been started.As one of the key techniques for 5G communication systems,massive MIMO attracts great attention in this domain.Therefore,the requirements for mobile communication antennas become higher and higher.To cover the multiple communication service bands simultaneously,broadband and multi-band antennas with compact size are in great demand and play an important role.Besides,the beamforming for large-scale mobile communication antenna arrays is a hot but also a difficult problem for the 5G communication systems.In consideration of the present situation and trend of mobile communication,this dissertation focus on the broadband and multi-band techniques for mobile communication antennas and the beamforming for large-scale antenna arrays.The major works and contributions of the author are summarized as follows:1.The electrical-magnetic composite antennas with broad band,multi-band and low profile characteristics are studied.In this dissertation,the operation principle and basic configuration of electrical-magnetic composite antennas are described.Then a low profile wideband electrical-magnetic composite antenna is designed.By using a folded radiating structure,the overall height of the antenna is reduced to 17 mm.And a wide bandwidth of 86.2% is obtained by employing an improved feed structure.A wideband dual-band magneto-electric dipole antenna is also presented.A U-shaped electric dipole is employed to generate the dual resonate frequencies and a folded magnetic dipole antenna which is realized by a shorted patch is introduced to achieve wide-bandwidth characteristic.The antenna is excited by a novel feeding structure for bandwidth improvement and identical radiation patterns in the E-and H-planes are observed.Besides,a very wideband electrical-magnetic composite patch antenna with simple feed is proposed as well.The antenna consists of a horizontal bowtie electric dipole with four matching tuning stubs and a vertical rhombic loop antenna.The antenna itself is dc grounded and has good performances over the operation bands.2.The broad band antenna with compact size for indoor distributed systems(IDS)is studied.The antenna consists of three top loaded coupling patches which are shorted to the ground plane by three strips,three radiation patches,a circular sleeve and a truncated cone feeding structure.An enlarged bandwidth of 152% and omnidirectional radiation patterns for the horizontal plane are achieved.3.The broadband and multi-band dual-polarized antennas with compact sizes for indoor MIMO communication systems are studied.Firstly,a low profile dual-polarized omnidirectional antenna is studied for broadband IDS.The proposed antenna is composed of an improved discone antenna for VP and a printed dipole array for HP.By loading two coupling structures,the antenna height is reduced to 80 mm and can be applied to several communication systems,such as 2G/3G/4G/WLAN.Secondly,a multiband dual-polarized omnidirectional antenna is studied.Two printed circular dipole arrays are employed for HP while a simplified discone antenna is used for VP.To realize a compact size,the two dipole arrays are fixed on the top and bottom of the VP element respectively and combined by a diplexer.So the HP element can operate at lower frequency band.Finally,the low profile dual-polarized antenna is tested in practical mobile communication systems,results show that by using the dual-polarized antenna,the performances for indoor MIMO systems are obviously enhanced.4.The beamforming of large-scale mobile communication antenna arrays for massive MIMO systems is studied.First of all,the Differential Evolution algorithm and its improved algorithm are introduced.Next,the structure and principle of the large-scale mobile communication array with 64 channels are analyzed.On this basis,a dual-polarized base station antenna element is designed for D band of TD-LTE.And an antenna array with 64 elements is proposed for theoretical verification of the beamforming method.And then,a 3D beamforming and optimizing method for the large-scale array with 64 channels is presented.By adjusting the beamforming results of the H and E planes for the proposed array,the 3D beamforming and optimizing method are realized.Finally,the optimized results are tested and verified theoretically and practically.Simulated and measured results show that the proposed beamforming method of large-scale mobile communication antenna arrays for massive MIMO systems can be widely used.