In order to realize a wideband RF source for cband and xband, an implement scheme of RF source was constructed based on the theory of PLL synthesizer. After introducing the synthesizer chips HMC983/984 and designing a wideband microstrip directional coupler needed in scheme, the parameters of LPF from simulation soft were obtained. By analyzing the design process of power and frequency resolution of RF source, the demands of soft control, filtering circuits, power supply design, input power of reference and feedback were mentioned, finally the design of the 5～10 GHz RF source was completed. The experiment revealed that the frequency error of the output signal was less than 0.001%, and the power flatness was not more than 4 dB, so the design achieved the expected specifications.