| Mobile communication networks depends on antenna electromagnetic wave radiation to achieve signal coverage.The function of antenna is irreplaceable and important.In the 2G era,simple application mode of single polarization(single channel)and dual polarization(dual channel)was widely used in antenna in this era.Under the requirement of the standard of TD-SCDMA in 3G era,8-channel dual-polarization smart antenna was gradually adopted.When enter into the 4G TD-LTE and 5G era,multiple-channel antenna array is becoming the standard.One of the most popular standard is 5G Massive MIMO antenna system in which 64T/R channel application mode is used.The antenna system's passive component is made of antenna array and antenna calibration network.Intelligent algorithm is adopted in the Massive MIMO antenna to accurately realize the feed amplitude and phase distribution in every T/R channel.So the required patterns of shaped beams can be produced.Antenna calibration network is a significant component which is used for detect and calibrate every T/R channel's amplitude and phase information.Its own performance determine the success or failure of the Massive MIMO antenna system.Further,it will determine whether the 5G mobile communication networks will succeed or not.Consequently,we will choose the Massive MIMO antenna calibration network as the research topic.Nowadays,5G is going to be commercialized,while 4G mobile communication will also coexist in the networks with 5G in the next several years.According to one of the popular practical application requirement: a wide band(2.3GHz~2.7GHz)64 T/R Massive MIMO antenna system covers the 4G B40 band(2.3GHz~2.4GHz)and 5G FR1 N41band(2.496GHz~2.69GHz).Therefore,we analyzed the application indicators and made clear about the 4 module and microstrip line scheme.We designed every single passive circuit components(Wilkinson power dividers and low coupling and high directivity coupler)with good performance.Then combined them together to form the 64 channel,wide band,low cost and easy debugging Massive MIMO antenna calibration network.Finally,we loaded this antenna calibration network into Massive MIMO antenna system.To solve the difficulty ofthe wide-band antenna calibration network's isolation problem,we designed a open stub which is equivalent to capacitance to compensate;Due to the high frequency and wide band,the lumped elements become divergent affected by parasitic parameters.We realized a TRL calibration circuit to improve it;We designed a split cavity to solve the problem of the chaos of the amplitude and phase and cavity resonance when loading the shield cover;As a result of structural material differences and processing,welding,assembling tolerances,the coupling degree become discrete.We raised a method of filling dielectric cylinder to fine-tune it.Finally,we manufactured the antenna calibration network and tested the main circuit performance indexes.The test results are consistent with the simulation and the antenna calibration network satisfies the actual Massive MIMO antenna well. |
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