X-band Frequency Synthesizer

The fantastic development of the electronic technology is bringing forward higher request for frequency synthesizer.All frequency synthesizers with highly pure spectrum, low phase noise and fast frequency switching speed have dominated development direction of the frequency synthesis technology. According to different application fields, the point emphasized of each system is also different.This thesis describes the basic structure, working principle, sources of spurious signals and characteristics of output spectrum of direct digital frequency synthesizer. Then the basic structure, phase model, frequency response and performance analysis for noise and spur of phase locked loop are presented. Combining the DDS and PLL technology can achieve both high frequency resolution and fast frequency switching speed hopping without degradation of spurious characteristics.The hybrid frequency synthesis technology called"DDS+PLL+frequency doubling"used in the subject has many advantages.Using this method,the merits of DDS such as super fine frequency resolution,high frequency accuracy and easy programmed can be in combination with excellent character of narrow-band tracing filter merits of PLL. Thereby,pure spectrum character of the frequency synthesizer in X-band can be realized. By adopting the hybrid DDS+PLL frequency synthetic technology controlled by MCU, the C-band frequency synthesizer has been devised. Then a frequency doubller make the output frequency expand to X-band.The functional realization of each module, some questions which must be pay much attention in the system design are represented and analyzed in detail.The hardware interface circuit of SCM and AD9850,the AD9850 serial working flow,the design of PLL,the design of C-band and X-band filters are introduced specially. According to the requirement of system,devices suitable to put up the circuit are chosed, carrying on the rational circuit overall arrangement and design of EMC. Phase noise result and picture of spectrum with spur are presented. Its specifications show as following: output frequency range 8.86~9.22GHz, phase noise-80dBc/Hz@10kHz, SFDR-50dBc. Finally, analysis of the result is given, and the existing problem as well as methods to resolve it are motioned.