Surface acoustic wave radio frequency identification tag (SAW ID tag) reader is divided into two catalogues of time domain sampling and frequency domain sampling. In the realization of SAW reader based on frequency domain sampling,a frequency sweeping signal source with good performance is indispensable.A frequency sweeping signal source has been designed based on DDS and PLL frequency synthesis technologies,its centre frequency, sweeping range and step frequency can be adjusted.Furthermore,a power amplifier circuit is added to amplify the frequency sweep signals.The signal source hardware circuit is fabricated,and the single frequency,the sweeping signal as well as the power amplifier module are tested respectively.The frequency locking process is analyzed. The test results show that the signal source has realized a center frequency of 940 MHz,the sweeping range changing from 933.75 MHz to 946.25 MHz,the step frequency of 125 kHz,and power of 15 dBm.