Investigations On Key RF Technologies Of 3.5GHz Digital Multibeam Array For 5G Massive MIMO Applications

Massive multiple input multiple output(MIMO)technology based on digital multibeam array is the core technology of fifth generation mobile communication(5G).In the array,each antenna element is followed with a RF transceiver.In this paper,for the massive MIMO applications in the 5G 3.5GHz band,some key RF technologies in the digital multibeam arrays are investigated.The major contributions of this dissertation are as follows:Firstly,a single RF channel is designed and implemented with low IF and shared local oscillator structure.The channel is designed and tested based on the densign and test of each module.The measurement results show that:the signal ranging from-30dBm to OdBm with the bandwidth of 200MHz can be transmitted.The flatness is 2.297dB within the 200MHz bandwidth when OdBm signal is transmitted.For the transmitter at 3.5GHz,the measured EVM is 1.6%rms and ACPR is-40.3dBc when input a LTE20 signal with OdBm transmitting signal;the measured EVM is 2.3%rms when input a 64QAM signal with 100MHz bandwidth.The receive channel can receive RF signal ranging from-85dBm to-25dBm with the bandwidth of 200MHz.The flatness is 1.555dB within the 200MHz bandwidth when receiving-25dBm RF signal.OIP3 is 28dBm which implys high linearity.The measured EVM is 0.911%rms at 375MHz by inputing a LTE20 signal when receivering the signal of-25dBm.The measured EVM is 2.6%rms at 375MHz by inputing a 64QAM signal with 50MHz bandwidth.The measured EVM is 2.5%rms at 375MHz by inputing a 256QAM signal with 50MHz bandwidth.Secondly,a 8-channel board and planar dipole antenna array are designed and implemented,the measured results show that:the consistency of 8 channels is good and all the performances can meet the requirements.Based on the calibration of 8 channels,the antenna and RF channel were tested together and the beams were synthesized in the digital domain.The measured results shows that the beam scanning and synthesis can be realized within the range of ±500.In the end,a standard 64-channel array structure is introduced,which consists of eight parallel boards and backplanes.