S. R. Davies

A 210–280 GHz sis heterodyne receiver for the James Clerk Maxwell Telescope part I: Design and performance

We describe the design and performance of a 210–280 GHz SIS heterodyne receiver built for use on the Maxwell Telescope. The mixer utilises a lead alloy SIS tunnel junction, mounted in 4∶1 reduced height rectangular waveguide, and is tuned with a backshort in 2∶1 reduced height guide. The receiver has a receiver noise temperature of <200K (DSB) across the RF band from 210–270 GHz, with a best noise temperature measured in the laboratory of 113K (DSB) at 231 GHz. A prototype version of this receiver was successfully operated on the telescope in May 1989. By direct intercalibration with a Schottky diode receiver we deduced a best receiver noise temperature of 140K (DSB) at 245 GHz. Discrepancies between this figure and that derived from broad band thermal load calibration are discussed in the accompanying paper (Little et al., 1992, this issue).

A 345 GHZ heterodyne receiver for the James Clerk Maxwell Telescope

In this paper we describe the design and performance of a low-noise 345 GHz heterodyne receiver. The mixer uses a lead alloy SIS tunnel junction mounted in reduced height rectangular waveguide and is tuned with a single backshort. Local oscillator power is provided by a broad-band Gunn oscillator which drives a frequency quadrupler. The heterodyne performance has been verified in the laboratory using a gas absorption cell. In November 1991 this receiver was successfully commissioned and by direct comparison with a Schottky diode receiver we confirm a best receiver noise temperature of 150K (DSB) at 355 GHz and a tuning range of 300 to 380 GHz. The receiver is now available as a JCMT facility instrument.

An SIS Receiver for the JCMT

A 220–280 GHz prototype SIS receiver system is currently being constructed, which will be tested on the JCMT in January 1989. The prototype receiver will act as a test-bed for developing a dualchannel common-user SIS receiver for the JCMT, tunable from 280–360 GHz, in a collaborative project between UKC, RAL and the Herzberg Institute of Astrophysics, Ottawa.

An SIS based 230 GHz receiver for Astronomy

A 230 GHz mixer receiver has been constructed using (Pb/In/Au) - (Pb/Bi) SIS junctions fabricated using the Dolan bridge method and thermal oxidation. The mixer block is of conventional design with reduced height waveguide and contacting backshort. Preliminary results indicate a receiver noise temperature <1000K (DSB).

800- to 900-GHz SIS receiver for molecular line astronomy

Recent astronomical observations of neutral carbon at 492 GHz have shown that its distribution is widespread in interstellar molecular coulds. Studies of the distribution and excitation of neutral carbon are of key importance in understanding the chemistry of such regions. Observations of CI at 809 GHz to complement those at 492 GHz would be of great importance in such studies. We are currently building as SIS receiver for the frequency band 800-900 GHz for use in observing submillimeter spectral lines, including CI. The receiver will be operated on the TIRGO infrared telescope, situated on the summit of the Gornergrat, Switzerland (altitude 10,390 ft). It is anticipated that this receiver will be mounted on the TIRGO telescope towards the end of 1996, or the beginning of 1997.

Low-Tc superconducting tunnel junction submillimeter wave receiver

A low Tc Pb alloy Superconductor-Insulator-Superconductor (SIS) tunnel junction heterodyne receiver has been constructed for astronomical use and tested over the frequency range of 400 to 540 GHz. Various alloy structures have been investigated in order to allow the production of small area SIS junctions with stable electrical characteristics and resistance to stress on cooling from 300 K to 4.2 K. Improvements in photolithography and thin film deposition techniques have been made that allow the fabrication of reliable sub-micron area junctions using suspended photoresist stencil and E-beam evaporation techniques. A single sub-micron area junction is mounted in a reduced height two tuner waveguide structure, which provides an optimum impedance match between the junction and the received signal. Performance measurements made with the receiver installed on the James Clerk Maxwell Telescope, Hawaii, show a total system double sideband noise equivalent temperature of 160 K at 460 GHz and 220 K at 490 GHz, measured in a 1 GHz instantaneous IF bandwidth centered at 4 GHz. The receiver demonstrates that Pb alloy tunnel junctions provide excellent sensitivity at submillimetre wavelengths and are sufficiently stable and reliable to allow use at a remote observing site.

A simple multiple beam lo coupler for SIS heterodyne arrays

The construction of SIS heterodyne imaging arrays for submillimetre wave-lengths requires multiple coupling of the local oscillator signal. The quasi-optical analogue of a multiple cross-guide coupler, employing 45° beam-splitters successively stacked along the local oscillator beam, allows for individual adjustment of local oscillator power to each channel. We analyse the coupling as a function of the focal ratio of the incident beams and the number of beam widths off-axis through which the coupler is extended, and describe a simple construction method to realise a compact and effective design.