Ultra Wideband Low Phase Noise Frequency Synthesizer Of Research

Modern war is a war of the science and technology,Along with the human disturbance factors in the military communication is more and more serious,The antiinterference performance of requirements for communication equipment is higher and higher. Among them, the frequency hopping communication technology has great superiority in anti-interference and anti-intercept. In Frequency Hopping communication system, Frequency synthesizer is its core component. Frequency synthesizer directly influences the performance of frequency hopping system ability of anti- interference and anti- intercept.This paper introduces the various implementation methods of frequency synthesizer in Frequency Hopping communication system. Some theory about transistor frequency multiplier、DDS and PLL is studied. According to their respective advantages and disadvantages, Combining of frequency multiplier、DDS and PLL, output of multiplier is the reference system clock of DDS, The output of DDS is the reference frequency of PLL,a frequency synthesizer is realized, with their advantages, but their shortcomings are avoided, So that the frequency synthesizer ’s overall performance is better. Among them, Frequency multiplier is designed by MRF851 BJT, Chebyshev bandpass filter is designed to filter harmonics, Multiplier’s output is the reference clock of DDS based on AD9910, As DDS has many spurs, a monolithic crystal filter is designed to filter DDS’s spurs whose band is only 30KHz; DDS’s output is the reference frequency of PLL based on HMC704LP4 chip, So PLL’s output is frequency synthesizer’s output. Frequency synthesizer’s output frequency design can be divided into a series of small segments in control program, Frequency Hopping in one segment can be very fast by only changing DDS’s control word, Frequency Hopping between any two segments will be longer by changing both DDS’s and PLL’s control words.Power system and cavity are designed for EMC, Each module is made of divided sections in cavity. Finally the synthesizer’s frequency range from 1850 MHz to 1850 MHz, Phase noise is better than-100 dBc/ Hz@10KHz,Spur suppression degree is better than-74 dBc,Frequency hopping time is less than 100?s,Frequency step is 10KHz。It can be seen that the overall performance of the frequency synthesizer is well,and frequency synthesizer meet the demand for the Frequency Hopping system.