Low Spurious Frequency Agile Frequency Synthesizer Technology

Low spurious and agile frequency synthesis is a very important technique in modern electronic systems, especially for modern communication system, radar, satellite and electronic countermeasure systems. It is a key technique especially in spread spectrum communication systems and radars, which can greatly improve the ability of anti-interference and processing gain of the system. Therefore, it is preferred by more and more electronic system designers all over the world. While, fast frequency hopping communication and agile radars were not fully developed up now, one important reason for this is that the synthesizer can not meet the requirement of fast-switching. Therefore, it is an important and urgent issue to have study on low spurious and agile frequency syntheis.This paper introduces the implementation of a Ku band fast-switching frequency synthesizer, which is a key component of coherent radar RF T/R front-end, based on intensive research on phase noise and spur theory and the technique of fast-switching frequency synthesis. By good frequency programming, circuits designing and making use of DDS, PLLs, FPGAs, the frequency synthesizer not only be implemented more easier but also has good performance of spectrum purity and switching time. Various modes of Chirp signal is produced by DDS in low frequency range (about 60MHz), and then it is converted to Ku wave band as transmission signal by three times up-conversion. In order to simplify the design, the LO for receiving is produced by two times up-conversion in a similar way, and LO for up-conversion is provided by two PLLs, one is a S-band fast-switching PLL synthesizer and another one is a ultra-low phase niose PLL synthesizer workes in Ku wave band. And the S-band PLL produces signal with technical index as follows: channel step: 5 MHz, frequency coverage: 400MHz, ultra-low phase niose and fast-switching among 30 MHz (≤10uS). From these index, it can be inferred that the technical index of whole component is greatly influenced by the technical index of the S-band PLL. Therefore, the implementation of the S-band PLL is one of the technical difficulty for this design.Technical Index eventually achieved: Phase Noise≤-96dBc/Hz@1KHz, Spur Level<-60dBc,Switching Time<10uS,channel step:5MHz and several modes of Chirp Signal. (Measured by Signal Source Analyzer FSUP-26)...