高速数传系统中的直接数字射频调制/解调技术

【作者】 邓建华；

【导师】 喻志远； 黄健；

【作者基本信息】 电子科技大学 ， 无线电物理， 2003， 硕士

【摘要】 本文所研究的课题是中国电子科技集团公司第十研究所“十五”预研项目：星载Ka频段300Mbps数传终端技术的一部分，即高速数传系统中的直接数字射频调制/解调技术。本人负责该课题的调制/解调方案论证、及分系统初步验证。首次采用以偶次谐波混频器为核心的直接数字射频调制/解调技术，之前国内尚未开展这方面的研究工作，本文对该技术进行了方案论证、电路实现和实验验证，这些工作为该技术的实用化奠定了较好的基础。文中特别分析了偶次谐波混频器的特性，首次提出了控制其相位特性的设计方法。这些都是本文的创新之处。本文采用先进的射频直接数字调制/解调技术方案。调制电路采用了以四次谐波混频器技术为核心的矢量调制技术，利用1/4载波频率作为本振信号，实现了对毫米波信号直接进行高速QPSK数字调制。在简化载波信号产生电路的同时，利用偶次谐波混频器固有的本振偶次谐波高抑制度特性，来抑制载波泄漏。解调方案同样采用四次谐波混频器在毫米波已调信号上进行载波同步。对调制/ 解调器射频电路部分，包括亚谐波混频器、检波器、功率分配/合成器和分支线耦合器基本原理进行了分析。讨论了利用EDA工具的电路设计技术，利用HP ADS、Ansoft软件完成了电路设计、仿真和制作了上述器件，并把电路仿真和场仿真以及测试结果进行了比较和分析。对方案中基带成形滤波、调制误差自适应补偿技术进行输入理论分析。利用FPGA作为基带FIR成形滤波的实现平台，论文给出了实现FIR成形滤波器的VHDL程序及仿真。调制/解调电路中，串并/并串变换、差分编/解码和抽样判决等数字逻辑部分是以CPLD作为开发平台，论文给出了实现上述功能的VHDL程序及仿真、测试结果。为了验证方案的可行性，进行了调制/解调有线联试，给出测试报告及进行性能评估，测试结果表明该方案是可行的。与中频调制方案和一般直接射频调制方案相比，本文所采用的技术大大简化了调制/解调设备，同时保持了优良的性能，对毫米波高速数据通信链路应用具有较大的优越性和广阔的前景。更多还原

【Abstract】 The topic of this paper is high-speed data transmission system, which is a part of an item of the 10th Institute of Electronic Science and Technology Corporation Group: space borne Ka-band 300Mbps data transmission system and technology. It is mainly concerned in this paper the schematic of modulation and demodulation.The paper adopted advanced RF direct digital modulation scheme. The modulation circuit utilized the vector modulation technology based on fourth-harmonic mixer. The LO frequency is only quarter of carrier frequency. Direct high speed QPSK digital modulation of millimeter wave signal can be realized with fairly simplified LO circuit. Carrier frequency leakage less than -40dB can be attained since good agreement of the two diodes antiparalleled in even-harmonic mixer is guaranteed inherently. Fourth-harmonic mixers are adopted in carrier recover in the modulation millimeter wave QPSK signal. In the part of modulation and demodulation, we analyzed the principles of harmonic mixer, detectors, power dividers/combiners and branch-line couplers. Especially, The characteristic of even-harmonic mixer is analyzed and design technique to control the phase characteristic of the mixer is presented. The mixer circuits are designed; the results of simulation and experiment test are compared and analyzed. Theory analyze of base-band shaping filter is delivered and adaptive compensation of imperfections in modulators are discussed. FPGA is used as platform of base-band shaping filter .The VHDL program and simulation of FIR shaping filter is given in this paper. In the modulation/demodulation circuits, CPLD is selected as platform of the digital logic part, which includes series-shunt/shunt- series transform, difference coding and sample verdict. In order to test the feasibility of the project, desktop test of modulation and demodulation as a whole is performed, the test report and characteristic evaluation are presented also. The test results demonstrated the feasible of the scheme. The technique researched in this paper will largely simplify the equipment of modulation and demodulation, and may find its application in millimeter wave in high-speed data communication link.更多还原