Phase Error Analysis and Optimization for Chirp Transform Spectrometer

In the field of deep space exploration, the rapid development of terahertz spectrometer has put forward higher requirements to the back-end chirp transform spectrometer (CTS) system. In order to simultaneously meet the measurement requirements of wide bandwidth and high accuracy spectral lines, we built a CTS system with an analysis bandwidth of 1 GHz and a frequency resolution of 100 kHz around the surface acoustic wave (SAW) chirp filter with a bandwidth of 1 GHz. In this paper, the relationship between the CTS nonlinear phase error shift model and the basic measurement parameters is studied, and the effect of CTS phase mismatch on the pulse compression waveform is analyzed by simulation. And the expander error optimization method is proposed for the problem that the large nonlinear error of the expander leads to the unbalanced response of the CTS system and the serious distortion of the compressed pulse waveform under large bandwidth. It is verified through simulation and experiment that the method is effective for reducing the root mean square error (RMSE) of the phase of the expander from 18.75° to 6.65°, reducing the in-band standard deviation of the CTS frequency resolution index from 8.43 kHz to 4.72 kHz, solving the problem of serious distortion of the compressed pulse wave form, and improving the uneven CTS response under large bandwidth.