A signal generator which comprises: a frequency synthesizer of a phase-locked loop structure, comprising: a first oscillator for producing first signal of a reference frequency; a phase detector, connected to the first oscillator, for detecting phase difference between the first signal and feedback signal (SFB), and producing second signal which represents the phase difference; a loop filter, connected to the phase detector, for removing unwanted frequency components of the second signal to produce third signal; a second oscillator, connected to the loop filter, for receiving the third signal, and producing fourth signal; and a frequency divider, connected between the second oscillator and the phase detector, for dividing frequency of the fourth signal, and impressing frequency-divided signal back to the phase detector as the feedback signal (SFB); such that a low-phase-noise signal (SLP) of the second oscillator is derived as an output signal of the synthesizer; a multiplier, connected to the synthesizer, for multiplying the output signal of the synthesizer; a band-pass filter, connected to the multiplier, for filtering multiplied signal output from the multiplier; and an amplifier, connected to the band-pass filter, for amplifying filtered signal output from the band- pass filter