X-band High-resolution Frequency Synthesizer And Design,

In application research of microwave system, X-band is an important frequency band. In radar system, X-band microwave is used for remote tracking, guidance, mapping, and airborne attacks; in addition, X-band microwave is also being widely applied in electronic equipments, such as satellite communications and military defense, etc. As a result, research on the X-band frequency synthesis technologies is of great significance.With the rapid development of wireless communications technologies, the request on frequency source is becoming higher in electronic system, and the main research direction of frequency synthesis technologies is to realize that of high frequency resolution, low phase noise, pure spectrum, steady frequency and quick transition. PLL (Phase Locked Loop) and DDS (Direct Digital Synthesis) are important frequency synthesis technologies. PLL has poor phase noise when the resolution is high, but it has better performance in spurious and higher output frequency; while, DDS has high frequency resolution, low phase noise, but its output frequency is low and spurious is serious. As DDS hybrid PLL is of advantages of the both, it has become an important technology of frequency synthesis.The paper is to realize a X-band high resolution frequency synthesizer, and its technical indexes are: the output frequency shall cover from 9.5GHz to 10GHz; the frequency resolution shall reach 100Hz; the phase noise shall reach -75dBc/Hz@1kHz and -85dBc/Hz@10kHz; the spurious level shall below -50dBc; the output power shall exceed 10dBm; and the frequency stability shall be±0.05ppm.Basic structures and work principles of DDS and PLL synthesis are introduced in this paper, and spurious sources of DDS are concluded, including phase truncation, amplitude quantization of sinusoid, and the transform error of DAC.Realization technologies of the frequency synthesizer are systematically summarized and analyzed, and specific realization scheme of the X-band frequency synthesizer that DDS employed to drive PPL are confirmed in consideration of the requirements on systematical technical indexes. Design works of the frequency synthesizer are completed, including segmentation of indexes, design of circuit diagrams, control program of PIC Single-Chip Microcomputer and design of Visual Basic's serial port correspondence program. In the design works, AD9910, a high performance DDS chip, with a resolution reaching 0.23Hz, is selected to generate the reference signal between 95MHz and 100MHz. Signals from the DDS are multiplied of frequency by the PLL between 9.5GHz and 10GHz, so as to reach a high frequency resolution, low spurious and high output frequency.Debugging and testing works of the X-band high resolution frequency synthesizer are accomplished.The testing displays that, the result satisfies the technical index requirements of X-band frequency synthesizer.