Abstract: A frequency synthesizer based on the waveform database for software defined multi-frequency surface wave sea-state remote sensing radar is presented.It can generate multiple pulsed frequency modulated continuous wave simultaneously or time-dividually,and the waveform,carrier frequency,initial phase and amplitude of which can be controlled independently.The performance of radar systems is improved greatly in the waveform types,amplitude and phase control,and frequency hopping time etc.The hardware and software structure is presented.Experimental results show that the phase noise of the frequency synthesizer is about-112 dBc/Hz at 1 kHz offset,which meets the stability demands of an HF surface wave radar for long coherent integration time.