Low Phase Noise Low Spurious Frequency Agile Ka-band Frequency Synthesizer

Due to the characteristics associated with Millimeter-wave ,it is applied in mm-wave radars,guidance,electronic countermeasure,mm-wave communication and remote sensing .As for mm-wave radars, they generally require frequency sources of high spectrum pureness and frequency-agile ability。This task was carried out just aiming at high–performance mm-wave sources.Direct analog frequency synthesis is an important way to yield high-performance frequency source. However it usually leads to high volume and fairly high spur level. Since commercial PLL IC came out, Phase-Locked-Loop frequency synthesis has become widely accepted. But when narrow frequency-step is required, the loop bandwidth has to decrease while cannot meet the demand of frequency-hopping speed. DDS(Direct Digital Frequency Synthesis)can just solve this problem, yet the output has an upper bound and high wideband spurs. According the demands with frequency source by mm-wave radars, this paper combined the first and third styles of frequency synthesis and developed a type of low-phase noise and spur,frequency-agile,mm-wave frequency synthesizer.Measurement has testified that triple-tuning of the two DDS output frequencies avoided frequencies with high spur level while ensuring the realization of total frequencies. The spur level is below-60dBc; The LFM output of the DDS was up-converted three times to Ka band, reducing phase noise, which is better than-91dBc/Hz@1kHz,-100dBc/Hz@10kHz, -104dBc/Hz@100kHz , decreasing frequency-hopping time which is less than 1μs. And together with the designing method introduced in paper, there are considerable reference value to latter scientific research work.