Network Analyzer Frequency Synthesizer Technology

With the development of communication technology, more and more RF measurement instruments are needed. But the status of RF instrument is not good. Western country's products occupy most of the market. These instruments are expensive, what's worse, many of the high precision instruments are prohibited selling to china. National's industry is blocked seriously. On product line, quantity of measurement instruments are needed, in many situations, there's no need for high precision instruments. Using high precision RF instrument is neither economical nor reasonable. So, low cost, good performance RF measurement instruments are needed. This project aim to research low cost, small size and fine resolution phase lock sweep source, which will be used in network analyzer.The difficulty of this project are realizing low cost, wide frequency band and fine resolution sweep frequency synthesizer. In order to realize fine resolution, fractional-N PLL or DDS technology can be used. But the former technology is more complex, bigger size and worse spur. Due to the development of LSI, we could use single chip DDS to get fine resolution and fast frequency hopping time. But DDS technology's shortcomings include low output frequency and serious spur when output wide band signal.According to the demand of the network analyzer, this paper analyzed DDS and PLL technique, and then combined them together, developed a type of fine resolution, low cost, wide band sweep source, which output 300KHz~1300MHz sweep signal with 1Hz frequency resolution. System include two main parts: one generates 2340MHz const frequency and the other make use of DDS+PLL technology realizing 2340.3MHZ～3640MHz phase lock signal with 1Hz resolution. Two signal are mixed to generate 300 kHz～1300MHz frequency sweep signal.Experiment has testified that, system's resolution achieved 1Hz. DDS output signal is multiplied directly, which make the system less complex, and cost lower. System's entire phase noise is better than -82dBc/Hz@10kHz, humorous spur is better than -31dBc.