Research On Technologies In Compact Antenna And Diversity Of Multiple Antennas For Mobile Terminal Devices

With the continuous development of mobile communication technologies,mobile communication systems with different bandwidths,different systems and different frequencies have met the needs of different business developments,forming a distinctive feature of multi-frequency and multi-system coexistence.According to this technical background,the operating frequency of mobile terminals is increasing,and which cause the number frequency bands and antennas of terminal to increase.On the other hand,MIMO,Massive MIMO and its arraying furtherly increase the number of RF systems and terminal antennas.For a mobile terminal with limited volume,the integration of many antennas in a small space brings about the problem of performance guarantee and performance improvement under device miniaturization.This dissertation target on the need of frequency diversity,space diversity and flexible array of the mobile terminal antenna,research on the basic theory and key antenna technologies of multi-band,miniaturization and decoupling,carried out a variety antenna prototypes of multi-band broadband antennas,compact antenna and high isolation,verified the correctness of the method.The main innovations are as follows:(1)A design method of planar structure broadband multi-band antenna is proposed.Methods based on the rectangular unit ultra-wideband monopole antenna structure,the inductive branch loading and the capacitive slot structure were introduced to achieve frequency control.In order to solve the problem of high efficiency of miniaturized antennas,we adopt a coplanar structure to improve the feeding efficiency of broadband multi-band.On this basis,a three-band adjustable wideband monopole antenna is designed and implemented with a bandwidth of 3.4 GHz and a minimum resonant frequency of 1.4 GHz,covering 4G LTE,5G,WLAN,WiMAX,DAB-L,etc.,current wireless communication system frequency bands.Further analysis and simulation of the surface current,by adjusting the branch and slot width,the frequency range can be further expanded,with good frequency adjustment capability.(2)A miniaturization method for multi-frequency multi-antenna is proposed.In order to increase the electrical length of the limited space,the method uses a "paper clip" structure as the main radiating element.To further enhance the controllability,we have developed an auxiliary radiation structure that achieves joint regulation of antenna frequency,bandwidth and efficiency.On this basis,a four-band miniaturized antenna(900 MHz,2 GHz,3.5 GHz and 5.8 GHz)was developed,and the antenna volume reached 15×25×1.5 mm3,which can effectively meet the needs of future thin multi-frequency terminal antennas;Introducing a capacitive double-sided double-belt line asymmetric feed loading method,a multi-band terminal antenna prototype was developed,which further reduced the antenna size(only 10×15×1.5 mm3),which was reduced to about 50%of the above methods.(3)A decoupling method and approach for coexistence of multiple antennas in a small space is proposed.The method uses the antenna ground as an extension unit to construct a new decoupling structure,which effectively utilizes the versatile effects of the ground.The simulation shows that the isolation between the antenna ports is greater than 15 dB,and the highest isolation is 30 dB,which can be used for effective isolation of compact antennas in small spaces,and which lay the foundation for the realization of multi-band MIMO.Further,we developed a ground slot decoupling structure to achieve reverse cancellation of leakage current and reduce crosstalk between antenna ports,thus developing a miniaturized high-isolation diversity antenna(2.5/3.6/5.3 GHz),the envelope correlation coefficient is less than 0.01.To increase the flexibility of isolation regulation,we introduced a metamaterial magnetic resonator structure to solve the dual-band regulation problem and developed a dual-band isolation enhanced antenna(2.6/3.5 GHz),the port coupling as low as-15 dB is achieved,and the minimum coupling is-30 dB,which verifies the high effectiveness of the isolation method.This dissertation proposes broadband multi-band,antenna multi-frequency miniaturization and multi-antenna decoupling methods,and develops the corresponding prototype antennas,which verifies the effectiveness of the method and lays a foundation for future sparsely distributed multi-band mobile communication terminal applications.