Millimeter-wave gas spectroscopy with SiGe BiCMOS transmitters and receivers for remote sensing and metrology

Abstract

In this thesis, SiGe BiCMOS transmitters and receivers are characterized for different applications in millimeter-wave spectroscopy. The goal is to analyze the applicability of these transmitters and receivers in two cases: Remote sensing, as for example from a small satellite, and metrology, in building a very stable frequency reference. The general performance of two versions of transmitter and receiver chips was analyzed. One is covering 220-255 GHz, the other is working at 222-270 GHz and 444-540 GHz. With both, wavelength modulation spectroscopy of methanol was successfully carried out. For further experiments, the first version was chosen due to its lower noise level and higher emitted power. For heterodyne spectroscopy for remote sensing, the noise temperature and Allan time of the receiver were analyzed and a setup for emission and absorption spectroscopy was built. With acetonitrile as trial gas, experiments were performed which allow predictions for the performance in mission operation. To build a stable frequency reference, a stabilization setup was developed to lock the transmitter to a rotational absorption line (molecular clock). The short- and long-term stability were analyzed. The short-term performance is limited by the system's noise and the parameters of the absorption line, whereas the long-term stability is mostly governed by drifts that stem from details of the setup. Best results with carbon monoxide showed an Allan deviation of 2.3E-11 at t=1000 s. Doppler-free spectroscopy, which was considered as an option to improve the short-term stability, could not be performed successfully. Starting points for improvement of the performance were identified for heterodyne spectroscopy in better isolation of internal receiver signals from each other. For the molecular clock, modifications in the setup are expected to improve the long-term stability considerably. In both cases, the temperature dependence of the performance is worth a deeper analysis.