L-band Frequency Synthesizer Applications,

This paper is a part of one project of China Electronics Technology Group Corporation the No. 10th Research Institute. The purpose is to realize the wide-band, high-speed, low-phase-noise and low-cost frequency synthesis in L band.This paper illuminates theory, structure, spectrum distribution, merits and defects, especially spurs of Direct Digital Synthesis(DDS), and it then introduces Phase Locked Loop (PLL) theory. By analyzing and comparing different schemes, we present a DDS+PLL scheme. DDS has the merits of high-resolution, high-accuracy, easily-control-of-frequency-variance. PLL has the excellent narrow-band-tracking-filtering characteristic. In this scheme, we combine the merits of DDS and PLL. The paper also points that in design we must stress on how to reduce the spurs, and puts forward the viewpoints on spurs distribution and the methods to control spurs.Then, the paper introduces the subject's target. Accoridng to the target and preceding analyses, we select AD9850 for DDS chip, PE3236 for PLL chip, and MCU PIC16F874 for loading control word and realizing control function. Afterward, we design and simulate the LC filter, microstrip low-pass filter and coupler, then implement the frequency synthesis. Finally,the circuit is tested and the target is obtained. The experiment results show that the DDS+PLL scheme is practicable.