Research On Key RF Technologies For Future Mobile Communications:Large Frequency Ratio Structure Reuse Technique And Asymmetric RF Modules

The rapid growth of wireless service data-rate requirement drives the development of new mobile communication techniques and the adoption of new frequency bands.At present,the sub-6GHz band is facing the problem of depletion of spectrum resources.The millimeter-wave band has abundant spectrum resources,but its path attenuation is relatively large,and more complex technologies are needed to improve its coverage.The coordination of sub-6GHz band and mm-Wave band with advanced massive MIMO technique are expected to perfectly solve the problems faced by the next-generation communication systems.This dissertation aims to study on the high-efficiency reusable RF structures for the low-high frequencies,and the novel techniques in the mm-Wave massive MIMO RF front-end module.In the network collaborated with the sub-6GHz band and the mm-Wave band,the highefficiency structure reuse techniques of passive components can significantly alleviate the space constraints on mobile terminals.However,in the case of large frequency ratio,the electrical size,operating modes and application ways of each frequency band are significantly different,which will lead to great challenges in the design of the structure reuse components.The first three chapters of this dissertation will focus on the research on the integrated large frequency ratio structure reuse device in the sub-6G and mm-Wave symbiotic system.Some important achievements,such as transmission,radiation,and frequency selection structures,are obtained.In the current 5G system,the full-digital massive MIMO architecture is adopted in the sub-6G band,while,the hybrid multi-beam massive MIMO architecture is used in the mm-Wave band.Although the hybrid multi-beam massive MIMO solves the problems of transmission distance,the system complexity and the cost in the mm-Wave band,it sacrifices the instantaneous coverage,and its application is basically limited to the fixed wireless access services,the coordination with the low frequency band is difficult.The asymmetric massive MIMO architecture based on the full-digital method releases the constraints of the symmetry of the transmitting and receiving beams,which means that the receiving and transmitting beams can be independently designed and optimized.In addition,the asymmetric massive MIMO architecture can obtain an excellent balance among these key indicators such as beam gain,quantity,coverage,system capacity,complexity,and cost.In an asymmetric full-digital massive MIMO system,each channel requires a complete frequency conversion and filtering circuit.In the mm-Wave band,due to the constraints such as size and performance,it is difficult to design high-performance miniaturized RF front-end modules.The last two chapters of this dissertation focus on the key techniques such as small and medium-sized filter components and miniaturized RF front-end for asymmetric mm-Wave massive MIMO base stations,and some creative research outputs have been achieved.The main work and contributions of this dissertation are as follows:1.A new transition is designed to achieve miniaturized transmission structure covering the sub-6G and mm-Wave bands.The transition from the grounded coplanar waveguide(GCPW)to the substrate integrated coaxial line(SICL)is realized by a three-dimensional grounded coplanar waveguide(3D-GCPW)structure.Compared with other SICL transition,this transition exhibits the characteristics of low processing sensitivity,high physical reliability,wide bandwidth and low insertion loss under the traditional PCB process.Experimental measurement was carried out to verify the feasibility and excellence of the relevant design.This work has been published in IEEE Microwave Wireless Components Letters.2.A new compact tri-band structure reuse antenna is proposed for the demand of highefficiency radiation in a sub-6GHz and mm-Wave bands symbiotic system.The antenna can operate in two sub-6G bands and one mm-Wave band,respectively.In order to further reduce the size of the antenna,a transition from microstrip line to substrate integrated waveguide is proposed to simultaneously excite different transmission modes in the sub-6G and mm-Wave bands.Thereby,the three-band antenna with a large frequency ratio can share the feeding port.Four longitudinal slots are etched on top of the substrate integrated waveguide to form a mmWave antenna operating at 28 GHz.At the same time,the outer conductor of the entire substrate integrated waveguide is reused into a monopole antenna that can operate at 3.5GHz and 4.9GHz,respectively.The feasibility of the proposed design has been confirmed by experiment.This work has been published in International Journal of RF and Microwave Computer-Aided Engineering.3.A new compact large frequency ratio multi-channel integrated filter with structure reuse method is proposed to meet the demand of compact filtering structure in a sub-6G and mmWave bands symbiotic system.The structure reuse method is based on mode composite transmission line(MCTL).The MCTL is composed of a fully shielded transmission line and a semi-open transmission line,wherein the outer conductor of the fully shielded transmission line can be used as the signal conductor of the semi-open transmission line to realize structural reuse.Compared with the traditional multi-channel filter,the design method proposed in this dissertation has higher flexibility in the selection of the center frequency,the filter bandwidth as well as the order of each channel.The work has been published in IEEE Transactions on Circuits and Systems II: Express Briefs.4.A filter design method based on high-accuracy coupling matrix response fitting is proposed for mm-Wave massive MIMO systems.Based on the proposed filter design method,low manufacturing sensitivity folded substrate integrated waveguide(FSIW)filters are designed.The air-loaded FSIW is used to realize the miniaturization of the longitudinal dimension of the filter structure,reduce the insertion loss,and the processing complexity.The out-of-band suppression performance and the processing sensitivity of common coupling structures in FSIW are analyzed.On this basis,an inductive coupling structure that takes into account out-of-band rejection and processing sensitivity is proposed.A high-accuracy fitting method of the coupling matrix response based on the alternating use of "J" and "K" converters is proposed.Two eighth-order FSIW filters with passbands of 23.5-28 GHz are designed.Their performances have been confirmed by experiment validation,and their compact sizes makes them be arranged according to the spacing of the antenna array elements in the MIMO system.5.A miniaturized RF front-end module with wide-angle coverage is designed for the asymmetric mm-Wave massive MIMO systems.Firstly,a miniaturized stepped ridge antenna is designed,which can cover 120° and 80° in azimuth and elevation,respectively.The designed mm-Wave transceiver channel spacing is the same as the antenna unit spacing,which greatly reduces the size of the antenna feeding network and the overall RF front-end size,and can avoid the use of complex feeding networks,thereby reducing insertion loss.Each transceiver module contains eight RF channels,and the modules can be infinitely stacked in the vertical direction to expand the array scale.The entire transceiver exhibits a wide IF selection range and shows good channel performance,which can provide a good scalable hardware platform for asymmetrical mm-Wave massive MIMO system verification.In the above works,3 first-author papers have been published and indexed in SCI database,and 2 first-author paper has published in the proceedings of international conference and national conference.