Research On Key Techniques Of Millimeter Wave Multi-beam Antenna Based On Broadband Compact Rotman Lens

With the advent of the Internet and the era of smart devices,the existing spectrum resources are becoming increasingly scarce,severely limiting the digital experience of end users,and people’s demand for high-density and high-speed communication systems is becoming increasingly urgent.The extension of the communication spectrum to higher frequency bands has become an inevitable trend in the development of mobile communication.As is known to all,the millimeter wave frequency band has considerable spectrum resources,which can well get rid of the dilemma faced by the current communication system.However,millimeter wave communication also has many problems,such as high transmission loss,weak diffraction and diffraction capabilities,etc.,which seriously affect communication quality and signal coverage.The multi-beam antenna system using beamforming technology can effectively enhance the equivalent radiation power of the antenna,reduce signal interference,and expand the signal coverage.It is an effective solution to the attenuation and blocking of millimeter wave communications.In addition,the multi-beam antenna system can also effectively use airspace resources to improve the system’s spectrum efficiency and communication capacity,effectively play the potential of the communication network,and create a high-quality communication network.In this article,millimeter-wave multi-beam antennas are considered as the research direction to explore key technologies of millimeter-wave multi-beam antennas suitable for 5G,and provide a broad development space for the further application of 5G communications in the future.The main research work is as follows:Firstly,aiming at the problem of high transmission loss in millimeter wave communication scenarios,an Antipodal Vivaldi antenna unit topology with semi-elliptical periodic distribution and split ring resonance stub loading is proposed,and a miniaturized antenna with high gain,broadband and backward suppression is designed and realized.By etching periodic elliptical slots on the radiation patch of the original antenna,a slow wave(SW)structure is constructed to expand the working bandwidth of the antenna and at the same time increase the antenna gain.The parasitic novel I-shaped metal patch at the antenna radiation flare acts as a director to improve the gain at the high frequency end of the antenna and ensure that the overall gain of the antenna works in a stable state in the band.The pair of metal split ring stub resonators is added on the ground to reduce the backward radiation and further improve the overall gain performance of the antenna.The gain of the antenna has been increased by more than 4 dB,the bandwidth has been extended by 2 GHz,and the backward rejection ratio has been increased by more than 4 dB.A planar array system has been designed to verify the superior array performance of the antenna unit.Secondly,aiming at the problem of large geometric size of the traditional Rotman lens,a broadband compact Rotman lens beamforming network structure in the millimeter wave frequency band is proposed,which realizes the design of a miniaturized millimeter wave Rotman lens.By using the power divider port to replace the traditional single-port feeding mode at the beam port of the lens,a highly directional beam is realized,which reduces the electromagnetic wave scattering inside the lens and the energy loss on the side wall of the lens while reducing the size of the beam port.At the lens array port,the Chebyshev multi-stub matching converter is used to optimize the original tapered output port structure.Under the condition of ensuring a large bandwidth,the output port size is reduced,and the size of the lens structure is compact.Finally,a broadband compact Rotman lens system with a geometric size reduction of more than 19%,a working bandwidth of 16.5-33.8 GHz,5 independent beams,and a±30° scanning range was realized.Finally,aiming at the mutual coupling problem in the application of Massive MIMO technology to the millimeter wave multi-beam antenna system,a miniaturized wide stopband MLR array isolation network is proposed,which significantly improves the isolation between antenna elements.According to the principle of open stub and coupled microstrip line,the wide stop band of MLR unit is realized,and the miniaturization of MLR unit is realized by using bent microstrip line structure,and the stop band bandwidth adjustment method of MLR unit is given.Finally,the MLR units are evenly arranged between adjacent antennas to suppress the mutual coupling of the arrays and improve the isolation between the antenna units(4 to 15 dB),and the decoupling effect of the design unit is verified in the binary antenna array and millimeter wave multi-beam antenna system,respectively.