| MIMO antenna system is widely used in the antenna module of mobile terminal devices.By providing multiple receive and transmit antennas to the device,the technology can transmit multiple signals in parallel in the limited frequency band resources,achieving the purpose of increasing channel capacity,reducing transmit energy consumption and eliminating multi-signal interference,which significantly improves the communication performance of the device.Among them,the miniaturized MIMO antenna system can effectively reduce the limitation of mobile terminal devices on space distribution,enhance the usability of mobile terminals,and make users have a better communication experience.However,the compact physical structure leads a mutual coupling effect between antenna elements,which mainly comes from the surface wave coupling and spatial radiation coupling generated by neighboring antenna elements.Therefore,ensuring the independence of the transceiver elements of a multiple antenna system in a limited space dimension is a challenge for the application of MIMO antennas in mobile terminals.This thesis is oriented to design a miniaturized MIMO antenna system applied in mobile terminals,and proposes a solution to the problem of taking into account the physical size and coupling effects in MIMO antennas,based on antenna theory and radiation mechanism,to study the methods to improve the performance of antenna in terms of bandwidth expansion and independence enhancement,the main work of the thesis is as follows:(1)A MIMO antenna for Wi-Fi 6E wireless router is designed.The small MIMO microstrip antenna system has a total size of32×32×1mm~3,and consists of four antenna elements with wideband characteristics.The-10 d B impedance matching operating frequency range is 5.07～7.37 GHz with an isolation of less than-11.0 d B in the operating frequency.The MIMO antenna adopts orthogonal spatial layout and double split ring structure to avoid coupling effects.The antenna elements are arranged orthogonally,and the maximum radiation directions are not related to each other to achieve the radiation diversity effect.The double split-ring structure is etched between the antenna elements to resonate the floor surface current inside them,which expands the operating bandwidth and suppresses the coupling effect,further enhancing the application value of the design.(2)An eight-port MIMO antenna is designed for smartphone applications.The narrow bandwidth of the microstrip antenna is improved by multi-mode resonance and coupling feed method.The antenna element operates from 3.30 GHz to 5.95 GHz,covering the n77,n78,n79,and WLAN 5G bands of 5G communication,with isolation better than 13.0 d B in the operating band.The antenna element spacing is compact,with a minimum spacing of 2mm,and the floor slot and ground branch are adopted to decouple together in the eight-port MIMO antenna system.The test results show that the isolation of the MIMO antenna is better than 10.0 d B and the ECC is lower than 0.1 in the operating frequency of 3.38～5.20 GHz.In addition,the MIMO antenna maintains similar performance to the above results in the single handheld state,which proves its good applicability as an antenna model for 5G communication terminal devices.(3)A broadband,low-coupling and compact antenna pair for smartphone applications is designed by combining research hotspot characteristic mode analysis method.The characteristic mode analysis guides the antenna structure adjustment to stimulate new resonance points and expand the antenna band potential.The-10 d B impedance matching bandwidth of the antenna is 3.23～5.24 GHz.With the proposed slots decoupled in the floor,the isolation between antenna elements separated only 2mm is less than-17.34 d B.After distance optimization,test results of the eight-port MIMO antenna constructed from four proposed antenna pairs show that its-10 d B operating bandwidth can cover the n77,n78,and n79 bands of 5G mobile communications with an ECC below 0.04 and antenna efficiency above 55%.This gives the MIMO antenna system excellent data transmission capability and can be widely used in 5G smartphones. |
