The Small Step Of The S-band, Low Phase Noise Frequency Source

With the continuous development of radar, communications and other modern electronic systems , frequency synthesis technology has become a key technology which is limiting their performance. Therefore, developing high-performance frequency synthesizers in modern communication technology has become an important research direction.The purpose of this research topic is to design a frequency source taking into account a small step, low phase noise and low spurious indicators. The system uses DDS-driven mixing PLL program. Finally, the feasibility of the program has been verified through the S-band hardware circuit.This paper describes the basic principles of several important modules-DDS, PLL, and voltage -controlled oscillator (VCO) in frequency source, Then makes a systematic analysis to the key indicators-phase noise in frequency source. On the theoretical basis of the analysis, the paper does a comprehensive feasibility study to the program, demonstrates the feasibility of the program. After that, the various parts of the circuit have been designed, including reference circuit, DDS circuit, VCO circuit, mixer phase-locked loop circuit and microcontroller circuits. The practical work also includes completing the preparation of the whole system control program. At last, the frequency source brings out the 2280MHz ~ 2380MHz frequency range, frequency hopping step of 1Hz signal output, and measured output signal phase noise at 10kHz is -89dBc/Hz. In the absence of electromagnetic shielding, so the theory and actual spurious indicators are quite differently.Finally, the paper analyzes the actual test indicators, sums up the problems existing in entire frequency source circuit, points out the direction for further work..