Abstract: A novel method to develop a frequency synthesizer with wide frequency coverage, fast frequency switching speed, and low phase noise is proposed. With the proposed method, the high performance of low phase noise and fast frequency hopping speed is achieved by combining Phase Locked Loop (PLL) and mixer. The Phase and Frequency Detector (PFD) current of the PLL is applied to compensate the nonlinear property of Voltage Controlled Oscillator (VCO) and to avoid the degraded performance due to loop instability. By this, a 11.1~13.1 GHz frequency synthesizer with frequency-step 10 MHz and loop bandwidth 600 kHz is developed. Experimental results show that the performance of phase noise is better than -83 dBc/Hz@1 kHz and its frequency hopping time is shorter than 10 μs.