A frequency synthesizer using a phase-locked dielectric resonant oscillator for the frequency band of 15GHz is provided to drastically reduce noises of a voltage source existing on a top surface of a substrate by arranging a varactor diode on a bottom surface of the substrate. A frequency synthesizer(900) using a phase-locked dielectric resonant oscillator for the frequency band of 15GHz includes a TCXO(Temperature Compensated Crystal Oscillator)(30) for outputting a signal having a basic frequency. A voltage control dielectric resonance oscillator(10) has a dielectric resonator and outputs a frequency by the dielectric resonator. The frequency synthesizer further includes a sampling phase detector(PD1), a first loop filter(40), a second phase locked loop, a mixer(70), and a band pass filter. The sampling phase detector outputs the difference between the frequency of the TCXO and the frequency of the voltage control dielectric resonance oscillator. The first loop filter filters the output voltage of the sampling phase detector so as to be zero and outputs the filtered voltage. The second phase locked loop is programmed so as to select a channel in a unit of a predetermined frequency by receiving an input from an OCXO(Oven Control Crystal Oscillator). The mixer mixes the output of the second phase locked loop with the output of the voltage control dielectric resonance oscillator. The band pass filter removes the zero phase frequency by passing only the sum frequency among the outputs of the mixer.
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