| With the continuous advancement and popularization of communication technology,millimeter wave communication systems are rapidly being updated and moving towards higher communication rates and communication quality.The next-generation millimeter wave communication system not only requires a large amount of data exchange in a short period of time,but also requires reliability and low cost for tracking and aiming and beam scanning technology.In order to meet the needs of millimeter wave communication and solve the problem of difficult tracking of moving targets,research on beam forming and adaptive tracking technology has been carried out.Different from the current point-topoint fixed target communication in the millimeter wave band,a millimeter wave moving target wide-angle tracking communication system based on direction retrodirective technology is proposed in this dissertation,focusing on solving the direction retrodirective technology issues.Direction retrodirective technology is based on an array composed of retrodirective antennas(RDA),which can align its own transmission signal in the direction of the incoming wave without knowing the location of the incident wave source.This technology relies on pure analog form to invert the phase gradient of the incident wave through the conjugate module,and then resynthesizes the wavefront through the beam forming network(BFN).Compared with traditional phased arrays and smart antennas,this array does not require complex digital signal processing(DSP)modules and phaseshifting networks,which avoids the processing speed limitation problem of DSP.Therefore,the retrodirection has the characteristics of fast response,simple structure,low cost,and high reliability.It is used in modern millimeter wave communications and wireless power transfer(WPT)and other fields,which has broad application prospects.The dissertation is to solve the key problems of high millimeter wave loss,high cost,inconsistent amplitude and phase of millimeter wave channels,and difficulty in testing.Functionally integrating retrodirectively automatic tracking with millimeter-wave highspeed communications,and combining key technologies such as antennas,devices,and testing to achieve long-distance communications.During the design process,we will conduct research on key technologies in millimeter wave communication systems such as direction retrodirective adaptive tracking technology,high-performance passive device design technology,and comprehensive improvement technology for amplitude and phase consistency of multi-channel links,to provide an application basis for millimeter wave mobile communication technology.The main contributions of this dissertation are summarized as follows:1.For the problem of moving target tracking,millimeter wave retrodirective communication technology is studied.The general phase conjugation principle,Van Atta array,heterodyne mixing type direction retrodirection and the relationship among them are theoretically analyzed,and a technology that combines direction retrodirection with millimeter wave communication is proposed.Through a multi-channel system topology composed of three mixing RF link channels including a high local oscillator mixer,the millimeter wave signal is phase conjugated,the wavefront is reconstructed,and the transmission wave in the direction of the incoming wave is adaptively tracked.Based on this architecture,a principle prototype of the millimeter wave retrodirective communication system was designed,a system with a retrodirective transceiver and a beacon transceiver was formed,and device estimation in links and index allocation were performed.In the preliminary verification experiments,the amplitude and phase consistency problems in millimeter wave links were analyzed,and corresponding solutions were proposed,laying a theoretical foundation for subsequent work.2.For beam scanning and agility problems,the millimeter wave retrodirective antenna technology based on multi-feed reflector is studied,and two designs of multifeed reflector antenna are proposed.For the first design,the array-fed parabolic cylindrical reflector antenna optimizes the array spacing of multiple feed elements,adjusts the irradiation power distribution of the reflector,and synthesizes the pattern and gain.The transmission adopts the form of array plus reflector to achieve wide-angle domain retrodirective beam coverage.The antenna has a retrodirective gain of 41.2 dB and a 3 dB compressed scan angle coverage of ± 22.5°.The reflection test value of this antenna in the 172～260 GHz range is lower than-14.5 dB,and the match is good.For the second design of high-gain double-fed parabolic reflector antenna,agile switching of high-gain beams is achieved by relying on different positions of the feed relative to the reflector.The gain simulation value reaches 49.9 dBi,and the port reflection test values are lower than-15 dB in the range of 200～260 GHz.The antenna achieves precise pointing of the agile beam at 2.86°,maintaining consistency between simulation and testing.In addition,the beam switching time is 31.69 ns,achieving rapid agility of millimeter wave beams.Finally,the gain converted using phaseless near-field planar measurement technology showed an error within 0.5 dB,which verified the feasibility of the near-field measurement technology.3.To solve the problems of high loss and high cost,high-performance technologies for key devices are studied.For the low-cost third harmonic mixer,it uses idle frequency recovery technology and reflection phase control technology to reduce losses through compact layout.Tests show that the mixer’s down-conversion loss is as low as 6.8～11 dB at 100～110 GHz radio frequency(RF).Simulated and measured LO/RF isolation are 41 dB and 37 dB respectively.The mixer has the characteristics of low local oscillator(LO)frequency,high isolation and low conversion loss,making it suitable for use in low-cost retrodirective systems.For high-isolation couplers based on coupling bridges,the isolation performance is improved through multiple branches.The isolation at the isolation port reaches 25 dB within 213～219 GHz,and the insertion loss of the transmission and coupling coefficient are both less than 1 dB.The phase lead of the passthrough port is close to the theoretical value of 90° compared with the coupling port,which verifies the high isolation technology of the device.4.Aiming at the problem of difficulty in ensuring amplitude and phase consistency,the test technology of millimeter wave retrodirective communication is studied.A prototype of the transceiver was developed,providing a principle verification platform for millimeter wave retrodirective communication.In 220 GHz band,the feasibility of adopting a power division and synthesis scheme for multi-channel amplitude and phase consistency testing and calibration was verified.When the transmitting and receiving distance is 100 meters,the retrodirective power compression is 3 dB in the range of 15°,and the retrodirective power compression is 10 dB in the range of 31°.The system implements retrodirective tracking,and the retrodirective transceiver will automatically form a beam along with the direction of the incoming wave to track the navigation beacon beam.Tests show that the system can maintain an error vector magnitude(EVM)of less than 20% and a signal-to-noise ratio(SNR)of more than 15 dB over a wide angle.And it can basically achieve adaptive tracking high-speed communication with the rate reaches10 Gbit/s of 30° coverage in the 213～219 GHz band at a distance of 100 meters. |
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