高精度时间频率同步在科学研究、国防安全等领域正发挥着基础性的重要作用。为了实现对高速隐身飞行目标的探测，分布式相参雷达（DCAR）正向着高频、宽带方向发展，由此对单元雷达间的时频同步精度提出了更高要求。而传统时频同步技术无法兼顾传递频率、节点数和同步性能。为此，本论文基于微波光子学研究时频同步及网络化技术以满足高频宽带DCAR的多节点皮秒级时间频率同步需求，并取得如下创新成果：1、针对基于频率混频的相位补偿技术中非线性失真恶化频率稳定度的问题，提出基于全光微波相位共轭原理的频率传递技术，避免了探测信号的二次谐波对频率稳定度的恶化，同时可自适应地消除光纤时延波动。理论分析了该技术方案的可行性及影响频率稳定度的因素。实验实现了20 GHz信号在20 km光纤环路上任意接入点稳定传递，频率稳定度达到10E–16/1000s。针对DCAR中远端本振的低相位噪声需求，提出基于锁相光电振荡器的微波本振传递方案，实验实现了10.8 GHz本振在6.8 km光纤环路上稳定传递，相位噪声达到 -110 dBc/Hz@10 kHz。2、针对单波长传输的频率稳定度受后向散射或光反射限制与多波长传输时受光纤色散限制的矛盾，提出基于“空分并行传输”思想的频率传递技术。并利用多芯光纤（MCF）的不同纤芯作为并行通道设计实现了毫米波本振传递网络方案，有效克服了单波长传输时后向散射或光反射对传递性能的限制，同时能够满足DCAR的多节点频率同步需求。理论分析了该方案的可行性和性能影响因素。实验实现了36 GHz毫米波本振在1.2 km干线型MCF网络上稳定传递，远端接收信号在6小时内时延波动不超过3皮秒，相对频率稳定度约为3×10E–17/20000s。3、针对实现时间信号光纤传递需要复杂的载波调制或专用编解码处理的问题，提出基于时频转换测量原理的光纤双向时间传递技术，通过啁啾混频和时频变换分析即可直接得到双向传输时间，避免了复杂的子载波处理。结合微波光子频率传递技术，设计并在20 km光纤环路上实验实现了三节点时频同步网方案，频率稳定度达到10E–16量级/1000s，时间偏差约为0.5皮秒。应用高精度光纤时频同步网实现了两单元微波光子分布式相参雷达实验系统，在实验室场景中获得了X波段全相参信噪比增益8.1 dB。通过全相参合成提升成像信噪比，可以对距离单元雷达6米远的三个静止角反射器进行清晰成像。

High-precision time and frequency synchronization is of fundamental importance to commercial activities, scientific researches, defense security and so on. At present, the advent of high-speed stealth targets promotes the development of the distributed coherence aperture radar (DCAR) with high frequency and wide bandwidth, which requires the higher accuracy on time-frequency synchronization. Traditional time and frequency synchronization technologies fail to strike a balance among the transferred frequency, the number of nodes and the stability performance. Herein, this dissertation aims to research and apply the microwave photonics-based time and frequency synchronization network technologies for the multi-node picosecond-level synchronization requirements of the high-frequency and wideband DCAR. The major innovative contributions are summaried as follows: 1. To avoid the deterioration of frequency stability caused by nonlinear distortion in the frequency mixing-based passive compensation schemes, an all-optical stable quadruple frequency dissemination scheme using photonic microwave phase conjugation is presented over a fiber-optic loop link, which can be free from the second harmonics interference of the probe signal and automatically eliminate the fiber-induced phase drift at the same time. The feasibility of this scheme and the factors that affect the stability are theoretically analysized. A demonstrated experiment is conducted that disseminates a stable 20 GHz frequency signal to two arbitrary remote sites located at a 20-km fiber loop link. The relative frequency stability of 10E–16 level at 1000 s averaging time can be obtained at every remote site. Furthermore, for the purpose of a low-phase-noise local oscillator (LO) required by radar units of DCAR, a stable microwave LO dissemination scheme based on a phase-locked optoelectronic oscillator (OEO) assisted by passive compensation is proposed, which can both cancel out the fiber-induced phase drift and purify the phase jitter of the received LO at the remote site. Experimentally, the phase noise of the remote 10.8 GHz signal is improved to about -110 dBc/Hz at 10 kHz offset with the rms phase jitter of 0.023 rad. 2. In order to simultaneously mitigate the effect of the backscattering or optical reflections in single wavelength transmission and fiber dispersion in multi-wavelength transmission on frequency stability, a stable frequency transfer technology based on “space parallel transmission” is proposed. Accordingly, utilizing different cores of a homogeneous multicore fiber (MCF) as parallel channels, a millimeter-wave (mm-wave) LO phase dissemination network is presented and demonstrated, which can effectively escape the backscattering and optical reflections. The dissemination network is able to meet the requirement of multi-node frequency synchronization in DCAR. In the experiment, a 36-GHz mm-wave LO signal is steadily disseminated through a 1.2 km seven-core fiber trunk network to multiple access sites. In 6 hours, the delay fluctuations of the mm-wave signals received at the remote site and the access site are both less than 3 ps. The relative frequency stability of around 3×10E–17 level at 20000 s averaging time can be realized in this stable phase dissemination network. 3. Moreover, a fiber-optic two-way time transfer based on the time-frequency domain transform (TFDT) measurement is proposed, aiming to dispense with complex carrier modulation or special codec processing that is necessary for existing time signal fiber transfer schemes. The TFDT can directly obtain the two-way transmission delay through only chirp frequency mixing and time-frequency analysis, which avoids complex subcarrier processing. Further, combining with the aforementioned stable frequency transfer technology, a three-node time and frequency synchronization network over a 20-km fiber loop link is presented and experimentally implemented. At 1000 s averaging time, the frequency stabilities at two remote nodes reach 10E–16 level and the time deviations are around 0.5 ps and 0.8 ps respectively. Based on the high-precision fiber-optic time and frequency synchronization network, a two-unit photonic DCAR experiment system in X-band is demonstrated. The signal-to-noise ratio (SNR) gains of 8.1 dB are obtained in the full coherence operating mode. Experimentally, three stationary corner reflectors that are 6 m away from the antennas of the unit radars can be clearly distinguished through full coherent synthesis.