| The RF front-end circuit connects the free space with the intermediate frequency signal.With the development of "miniaturization,integration,and high performance" of modern communication systems,the performance and size of RF circuits are also increasingly required.The performance of the antenna and filter plays a decisive role in the performance of the communication system.The traditional method is to cascade the filter and the antenna to process the signal,but this method will cause the impedance mismatch between the devices and the circuit size is large.The integration of antenna and filter is designed as a filter antenna.This antenna has both radiation and filtering functions,and it also realizes the needs of integrating and miniaturizing RF circuits.Therefore,it has great research significance and application value.With the development of modern radio communications and the arrival of the fifth generation(5G)mobile communications,multi-input multi-output(multi-input multi-output,MIMO)technology has become one of the core technologies of 5G communication due to its advantages in resisting multi-path decay,suppressing common channel interference,and increasing channel capacity.In the narrow space of mobile terminals,the strong coupling between antennas and each other produces greater interference,which will seriously affect the normal operation of the MIMO system.Therefore,it is very important to study how to improve the isolation between multiple antennas in MIMO system.With the rapid development of communication technology,the demand for antenna performance is getting higher and higher.In an antenna system,one or more of the antenna parameters such as the frequency,orientation,polarization,etc.of the antenna are changed by adjusting certain devices with variable state and changing some parameters of the antenna.The antenna is called a re-configurable antenna.The re-configurable antenna has the advantages of small size,flexible and variable function,and can adapt to the requirements of modern communication systems.Therefore,this kind of antenna has great research significance.In this paper,the design and implementation of MIMO filter antenna and re-configurable filter antenna working in 5G communication frequency band are studied.The main work and achievements can be summarized as follows:(1)A MIMO filter antenna working in the 5G communication frequency band is designed.The filter part of the designed antenna adopts an equal-length coupling transmission line structure,and two controllable transmission zeros are introduced through the resonance of the equal-length coupling transmission line,so that the MIMO antenna achieves better filtering characteristics,and the radiation part of the antenna adopts a T-type gap antenna.In addition,the structure of the two antenna elements placed vertically reduces the coupling between the antenna elements caused by space waves.For the coupling caused by the surface waves of the floor,the joint is suppressed by opening the seams on the floor.In the end,it is known from the processing tests that the MIMO filter antenna has a working frequency of 3.5 GHz and the edges on both,sides of the central frequency are steep,that is,the filtering characteristics of the antenna are good,and the port isolation between the two antenna units is greater than 22dB.The filter antenna has All directions radiation characteristics,And the overall size is small,suitable for use by mobile terminals.(2)A radio frequency switch is designed.The PIN tube of the selected model SMP1340-079LF is used as the control device of the switch circuit,and the radio frequency switch and the corresponding bias circuit are designed using a parallel structure.(3)A frequency re-configurable filter antenna is designed.The filter antenna has a switched integrated feed network,which can be switched between UWB/5G communication systems.The integrated feed-in network consists of a 50Ω micro-strip line and a open-loop band-pass filter.Using micro-strip feed,different paths are selected through radio frequency switches to achieve the UWB band in double sinkhole waves(in 3.3 GHz-3.6 GHz and 4.8 GHz-5.1 GHz),3.5 Frequency re-configurable between the frequency band of the GHz 5G system and the frequency band of the 4.9 GHz 5G system.The results of processing the RF switch control network and the re-configurable filter antenna show that the antenna can switch three different operating States,and the antenna can basically achieve the characteristics of omnidirectional radiation. |
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