Dimethyl ether (CH3OCH3) is a well-known interstellar molecule with a large abundance in hot core regions. We have measured many rotational-torsional transition lines of this molecule in the 100-550 GHz frequency range using two experimental techniques: a klystron-based traditional millimeter-wave spectrometer and a new fast scan spectrometer (designated "FASSST") with a voltage-tunable backward wave oscillator. The lines arising from the ground vibrational state have been combined with previous data, mainly at lower frequencies, to form a global data set consisting of over 1600 lines that have been assigned and fitted by an effective Hamiltonian method. The spectral constants obtained from the fit allow us to predict the frequencies of almost 6000 additional lines of dimethyl ether through 600 GHz.
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