Research And Design On Key Devices Of TD-LTE/5G RF Front End

TD-LTE(Time Division Long Term Evolution)is a fourth generation(4G)mobile communication technology and standard developed jointly by major global enterprises and operators covered by 3GPP,which has been widely used.Fifth Generation(5G)mobile communication technology is a new generation of mobile communication system developed for the demand of mobile communication after 2020.According to the 5G promotion deployment proposed by Ministry of Industry and Information Technology and the 5G commercial plan of the three major operators,China will start 5G network construction in 2019 and officially launch commercial services as soon as 2020.As a new generation of mobile communication technology,5G inherits the communication technology and standards of TD-LTE and will be in a long-term coexistence with TD-LTE,therefore,in order to make full use of communication system resources,ensure smooth communication and improve communication quality,it is necessary for TD-LTE and 5G to work together.MIMO(Multiple Input Multiple Output)antenna,electrically tunable filter and low noise amplifier are important components of the RF front end of TD-LTE/5G system.Therefore,the design and implementation methods of MIMO antenna,electrically tunable filter and low noise amplifier used in TD-LTE/5G system are studied in this paper.The following results are obtained:1.In this paper,a dual-band mobile terminal MIMO antenna is designed using a dual-sided strips monopole structure.Because space wave is one of the main factors that cause the coupling between MIMO antenna elements,theoretically the two antennas perpendicular to each other are completely mismatched,that is,the signal can not propagate between the two antennas.Therefore,the two antenna elements with multi-branch on both sides are tilted 45 degrees to make them perpendicular to each other.At the same time,the floor branches are added between the two elements to further improve the isolation between MIMO antenna elements and reduce the correlation between the received signals of the two antenna units.For another factor causing the coupling between MIMO antenna elements,the floor surface wave is suppressed by slitting the floor.The processing test results show that the MIMO antenna works at 2.2-3GHz and 3.4～3.9GHz;the isolation degree between the ports is greater than 15dB in low frequency band and 18dB in high frequency band;the low frequency gain is 2.2dBi and the high frequency gain is 2.5dBi;it has omnidirectional radiation characteristics and meets the design requirements of MIMO antenna for mobile terminals.2.Based on the working principle of E-type dual-mode resonator and the design theory of constant absolute bandwidth,a dual-frequency adjustable bandpass filter with independent tunable central frequency is designed by adding a varactor to the E-type dual-mode resonator,and the absolute bandwidth is constant in the process of tuning the central frequency.By introducing multiple transmission zeros in the way of source/load coupling,the filter achieves good passband selectivity and wide-band harmonic suppression.The processing test results show that the first passband can be tuned in the range of 2.59～2.75GHz,and the bandwidth is maintained at 50±5 MHz,insertion losses are 6～4.2dB,stopband suppression is 35dB@10%f1;the second passband can be tuned in the range of 3.5～3.65GHz,the bandwidth is maintained at 100±5 MHz,insertion losses are 3.8～2.9dB,stopband suppression is 20dB@10%f2;and the harmonic suppression is greater than 20 dB in the frequency range of 1～5.5 GHz.3.A two-stage broadband low noise amplifier(LNA)is designed using the ATF series pHEMT(Pseudo-Crystal High Electron Mobility Transistor)of Anhuagao Company.In order to obtain broadband characteristics,the parallel resistance negative feedback structure is adopted.The input matching network of each stage adopts a matching network with high Q value,and the output matching network uses a matching network with band-pass characteristics to filter out out-of-band harmonics as far as possible.The processing test results show that the working frequency band of the low noise amplifier is 1.6-3.6GHz,the maximum noise in the band is 2.6dB,and the in-band gain is 24±1 dB..The results show that the designed MIMO antenna,electrically tunable filter and wideband low noise amplifier basically meet the design requirements.