High-precision fast scan millimeter- and submillimeter-wave spectroscopy

New spectrometers based on the direct digital frequency synthesizers are presented. The rate of molecular spectrum recording is up to 100 GHz/h with a high accuracy of measuring transition frequencies (the measurement error for isolated spectral lines lies within 0.002 MHz provided that the signal-to-noise ratio is 50 or greater). In addition the Lamb dip measurements are applied to improve spectral resolution and to obtain accuracy better than 0.001 MHz.