Abstract: A Ka band frequency synthesizer which has been achieved by combing the LTCC technology with the frequency synthesizing technology has been presented in this paper. Low phase noise and high frequency resolution have been achieved simultaneously by adopting double ring structure with fractional N division. And combing with LTCC technology it can improve the integration level and realize the goal of miniaturization when the active elements are mounted on the surface and the passive elements are integrated inside the substrate. The output frequency of this frequency synthesizer is from 34.8GHz to 35.2GHz, frequency step is 2MHz. phase noise is -75dBc@1kHz, -80dBc@10kHz, -90dBc@100kHz. The area of this frequency synthesizer is only 42mm×49mm through proper arrangement. The area of this frequency synthesizer has been reduced 37% compared to reference 2.