Investigations On Millimeter Wave Multibeam Antenna Arrays

With the explosion of the data in wireless communications,the system requirements of the fifth generation mobile communication(5G)cannot be met at conventional cellular frequencies,includinga data rate on the gigabit per second(Gbps)level,a latency time on the millisecond level.However,there are a lot of undeveloped spectrums in the millimeter-wave(mmW)frequency band.Thus,millimeter-wave communication systems have attracted a lot of research interest.In 5G communication systems,massive multiple-input multiple-output(MIMO)is another key enabling technologie: a number of antennas focus energy into smaller regions of space to improve the spectral efficiency and reduce the interference levels.Multibeam antenna is a good choice to enable the massive MIMO technology.The dissertation focuses on the research of the multibeam antennas based on active,passive,hybrid beamforming technologies applied in 5G mmW massive MIMO systems.It is organized as follows:Chapter one focuses on the digital multibeam array antenna.A novel full-digital multibeam array with a one-dimensional(1D)multilayered planar lens is proposed.The array consists of 16 dual-exponentially tapered slot antenna(DETSA)elements arrayed in the H-plane of the elements.Each element is integrated with a radio frequency(RF)receiver,an intermediate frequency(IF)chain and an analog-to-digital converter(ADC).A group of high gain radiation beams with narrow beamwidths and spatial coverage can be generated in the H-plane by phase shifting in the digital domain.A novel one-dimensional(1D)multilayered planar lens which transforms the spherical wave into a plane wave in the E-plane is proposed to narrow the beamwidth and increase the beam gain.Furthermore,the distribution of the phase shifting units in the planar lens is optimized to reduce the scanning loss of the array introduced by the lens.Meanwhile,the two-dimensional beam steering,the calibration and the verification of the synthesizing weights are discussed in detail.Part of the work in this chapter has been published in IEEE Transactions on Antennas and Propagation and applied for a patent.Chapter two focuses on the multibeam antenna based on quasi-optical beamforming method.An mmW multibeam folded reflectarray antenna(FRA)is proposed.By integrating the feeding network in the substrate integrated waveguide(SIW)form,multiple sources and reflective patches in a two-layer substrate board,the structure of the antenna is simplified and the manufacturing precision is improved.Feeding by novel SIW series-fed aperture-coupled patch antenna arrays,multiple high gain beams with narrow beamwidths and-3dB beam crossing-level are generated.A bifocal design methodology is used for improving the beam coverage and reducing the scanning loss.A nineteen-beam prototype consists of three sevenbeam FRAs with a ±30° spatial coverage is designed,fabricated and measured.The test results show that the 19-beam antenna at 42 GHz band has the advantages ofhigh gain,lowprofile,wide spatial coverage and having no cover blind spot.Part of the work in this chapter has been published in IEEE Transactions on Antennas and Propagation and applied for a patent.Chapter three focuses on the multibeam antennas based on passive beamforming networks.A broadband 8-beam tapered slot antenna(TSA)array is proposed and implemented by PCB technique.It is fed by 4 × 8 modified Butler matrices.SIW self-compensated phase shifters are used in the structure.The 8-beam antenna is consist of two sub-arrays which are tilted,respectively.The radiation beam cross points of one sub-array are covered by the beam pointing direction of the other one to address the covering null points between high gain beams.Besides,by feeding to a one-dimensional planar lens,the gain of all radiation beams is further improved and the sidelobe is reduced.Some designs in this chapter have been published in IEEE 7th Asia-Pacific Conference on Antennas and Propagation and achieved the Student Paper Award of APCAP2018.Chapter four focuses on the digital-analog hybrid Multibeam Antenna array.A 128-channel millimeter-wave digital-analog hybrid multibeam antenna array is proposed.The two dimensional beam steering of the array is achieved by two orthogonal one-dimension(1-D)beamformers:The multiple beams in the vertical direction is generated by a 1-D passive beamforming network,e.g.an 8-port Butler matrix.And the beam scanning in the horizontal direction is achieved by a 16-channel,1-D digital beamformer.The two-stage down converter scheme is adopted.The system consistsof 128 radio frequency(RF)receivers,intermediate frequency(IF)amplifiers,power dividers,and two local oscillator modules.256 elements are used in the array.The scan coverage is larger than ±45° in the vertical direction and ±30° in the horizontal plane with the scan loss less than 5dB.The limited coverage,high cost and complex algorithms in the conventional hybrid beamforming array are addressed by the novel multibeam array.Moreover,the gain and the side lobe levels are improved by reducing the coupling effect in the E-plane.And the measurement and calibration of hybrid multibeam array are discussed.Some works in this chapter are submitted to IEEE Transactions on Antennas and Propagation.