For the purpose of solving the problems that the quantity of airborne navigation equipment simulator is large, which is not conducive to the integration of automatic test system, a generalized signal simulator is designed, and the ADF4351 is used as the core to constitute the local oscillator signal source, realizing wide frequency band and frequency adjustable function. First, the basic principles and working characteristics of the ADF4351 are analyzed. Then, the detailed design method of the frequency synthesizer is introduced. Through the USB peripheral controller chip CY7C68013A, the host computer controls the ADF4351 to produce the specific frequency RF output. At last, with altimeter signal simulator for example, the phase noise and spurious suppression of the 4.3 GHz RF output are measured by a spectrum analyzer. Experiments show that the designed frequency synthesizer can achieve low phase noise and stable frequency output from 35 MHz to 4.4 GHz.