Computer-Controlled MM- and Sub-MM Wave Josephson Spectrometer with a Planar Integrated Front End

MM-wave spectrometers and receivers with wide tuning bandwidths are needed for the analysis of gases as well as for radioastronomy and EMC-measurements. Up to now, broadband Fourier transform spectrometers (FTS) with a high-precision mechanical set-up and movable mirrors or narrow-band microwave spectrum analysers (MSA) with mixers for each waveguide band are used for these purposes. Divin et al. proposed a very sensitive spectrometric method with an extremly wide tuning bandwidth /1/. No mechanical tuning and no changing of mixers is necessary. The dc voltage-current characteristics of a point-contact Josephson junction is deformed by the incident radiation according to the ac Josephson effect. The spectrum of the radiation is obtained by applying an inverse Hilbert transform on the resulting deformation of the dc characteristic. First experiments were performed. A spectrum consisting of a broad single line at 600 GHz was investigated /1/ and two narrow lines at 68 and 70 GHz were observed simultaneously in /2/. A planar integrated front end, compared to the three-dimensional set-ups used in /1/ and /2/ has the following advantages: - greater tuning bandwidth - better reproducibility - integration of a planar Josephson junction, which is mechanically more stable and needs no adjustment after each temperature cycle. - reliable contacts between the components of the front end. Therefore, a mm-and sub-mm wave Josephson spectrometer with a planar integrated front end was designed and built. This is described in this paper.