  In this paper, the filter- and frequency-to-time mapping (FTTM)-based
photonics-assisted time and frequency acquisition methods are comprehensively
analyzed and the accuracy and resolution limitation in the fast sweep scenario
is broken by broadening the filter bandwidth. It is found that when the sweep
speed is very fast, the width of the generated pulse via FTTM is mainly
determined by the impulse response of the filter. In this case, appropriately
increasing the filter bandwidth can significantly reduce the pulse width, so as
to improve the measurement accuracy and resolution. FTTM-based short-time
Fourier transform (STFT) and microwave frequency measurement using the
stimulated Brillouin scattering (SBS) effect is demonstrated by comparing the
results with and without SBS gain spectrum broadening and the improvement of
measurement accuracy and frequency resolution is well confirmed. The frequency
measurement accuracy of the system is improved by around 25 times compared with
the former work using a similar sweep speed, while the frequency resolution of
the STFT is also much improved compared with our former results.
