A wide Ka-band frequency agility synthesizer with low phase noise and high frequency stability is presented in this paper, which serves as the emission source of transmitter and the local oscillator (LO) of receiver in fully electronic millimeter wave (MMW) imaging system. In order to improve operating frequency and shorten hopping time, a novel method is proposed in this synthesizer. By mixing direct digital synthesis (DDS) with multiple phase locked loops (PLLs) and multiplying the mixed signal, a high output frequency with low phase noise and rapid frequency hopping is realized. The experimental results show that the frequency synthesizer achieves frequency resolution of 1 MHz from 27 to 32 GHz and phase noise of -95 dBc/Hz at 10 kHz carrier offset. In addition, the frequency switching time is 2 μs, and broadband spurs do not exceed -60 dBc.
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