In the application technology of terahertz spectrum analyzer, Chirp transform spectrum analysis uses surface acoustic wave filter, which can guarantee the parameters of intermediate frequency and resolution, and meet the strict requirements of stability and power consumption in deep space exploration. However, the Chirp transform spectrum analyzer in China can only process 400 MHz bandwidth input signal, which can not fully meet the application needs. In order to improve the bandwidth, a frequency analyzer with 1 GHz bandwidth and 3.2 GHz center frequency is designed in this paper. The digital part is implemented and the results are analyzed and validated.