| The low frequency spectrum resources are increasingly scarce with the development of communications and radar technology. There are two advantages for the rapid development of millimeter-wave communication:rich spectrum resources and equipment miniaturized. Frequency synthesizer is the key component of communication equipment; its frequency stability and accuracy affect the overall performance of the system directly. As we are manufacturing the communications equipment of Ku frequency band, this paper mainly discusses the research design the frequency synthesizer in it.Firstly, Frequency synthesizer has three ways to achieve:Direct frequency synthesis, PLL frequency synthesis, direct digital frequency synthesizer. They were applied to the various needs of different project scenarios based on their advantages and disadvantages. Secondly, analysis PLL frequency synthesizer and direct digital frequency synthesizer output spectrum according to the requirements of system, and analyzed the key indicators with a variety of mixed frequency synthesis way. Focus on the effect of each frequency synthesizer with phase noise, frequency step, and spurious. Finally, the system frequency synthesizer was realized by the way of DDS excitation PLL and mix with PDRO. Simultaneously, by variable frequency clock and calculating the proximal stray appears to reduce spectrum spurs. On the basis of this program, combined with the selection of devices, the simulation proved the method in this paper is useful and suitable. ADS and HFSS are used for part circuit design and simulation optimization. At last, Protel, AutoCAD, SolidWorks and other software are used for circuit and structural design, completed small step Ku-band low phase noise frequency synthesizer low stray preparation.Eventually, the system realizes Ku-band 1Hz step, phase noise of less than -90 dBc/Hz @10kHz, better than 60dBc spurious suppression of the LO signal output, and having an output bandwidth of 1.5GHz. |
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