A fast scan synthesizer-based microwave spectrometer

For a long time it was generally agreed that microwave PLL-spectrometers are rather complicated devices which allows to record molecular spectra rather slowly and in rather narrow frequency range. Therefore for full frequency range scan some alternative techniques were applied. There are two rather similar approaches: the so called RAD-3 spectrometer [1] and the Fast Scan Submillimeter Spectroscopic Technique (FASSST) spectrometer [2, 3]. Both these instruments based on application of BWO have essentially common feature: they do not use a phase-locked system for BWO frequency stabilization. Main advantage of both above-mentioned techniques is the possibility to obtain wide-range frequency scan. In addition FASSST spectrometer allows to record molecular spectra very rapidly. However the absence of phase-locked system leads to a principal disadvantage: both spectrometers provide rather low measurement accuracy. Typically, the uncertainties of the frequency determination of spectrometers without phase-locked system are about two orders of magnitude worse than those of PLL-spectrometers.