A novel low phase noise frequency synthesis scheme based on Radio Frequency-In-Package (RF IP) is proposed. The multiple frequency points are generated by the comb generator, the frequency band is selected by the switching filter, and the frequency spectrum shifting is performed by the secondary mixing, therefore, the broadband coverage of Ka-band is realized. The integration method of three-dimensional System-In Package (3D-SIP) compensates for the disadvantage of traditional direct frequency synthesis in achieving miniaturization. A small step variation of 100 MHz is achieved through a frequency divider and multiplier. This scheme can achieve a phase noise of -99 dBc/Hz@1 kHz, compensating for the disadvantage of Direct Digital frequency Synthesis (DDS) excited Phase-Locked Loop (PLL) small step frequency synthesis in achieving low phase noise. This frequency synthesizer has the advantages of miniaturization and low phase noise, has strong engineering application value, and can be expanded for use in various communication and radar systems.