In this paper, PBG structure and feedforward circuit has been used to suppress the phase noise of the oscillator. Microstrip line resonator have low Q, but we can obtain high LO power by feedforward circuit and improve the resonator Q by the PBG, simultaneously. The proposed oscillator which uses PBG and feedforward circuit shows 0${~}$20 dB phase noise reduction compared to the conventional oscillator. We have obtained -115.8 dBc of phase noise at 100 kHz offset from 2.4 GHz center.