ALMA BAND 2 EVALUATION RECEIVER AT THE 12 m TELESCOPE David Forbes, Thomas Folkers, Robert Freund, Eugene Lauria, Martin McColl, Mark Metcalfe, George Reiland, Lucy Ziurys Arizona Radio Observatory Tucson, AZ ARO 12m Antenna Objective • Evaluate the performance of the latest cryogenic MIC/MMIC amplifier technology as compared to the well established SIS technology for the 4mm band • Provide a direct comparison of each of the technologies with observational data • Done by constructing an insert for each type of amplifier (MIC/MMIC) and installing each opposite of an insert using an SIS mixer • These mixers have been used at the 12 m over the past 20 yrs. • Deep integrations done at the J = 1→0 H2CO line at 72.8 GHz Receiver Architecture SIS SIS MIC MMIC Receiver Architecture 4-8 GHz 1st IF USB 1.5 GHz 2nd IF downconverter E-band downconverter Needed for MMIC Amplifier LSB SB selector switch 1.5 GHz IF to Backends LO 1.5 GHz IF to Backends SIS Mixer SIS LO IF Amplifier Dewar Boundary • SIS mixer channel operates in singlesideband mode • Amplifier channel utilizes sidebandseparating mode Legacy 68 - 90 GHz 12 m Insert • SIS mixer • Uses (2) backshorts to provide SSB operation • 1.5 GHz IF RF Amplifier-Based Inserts E-band Downconverter Architecture WR-12 Quadrature hybrid coupler MAC Tech. C7256 4-12 GHz quad. hybrid coupler Millitech MCA-12-120187 Front end signal from amplifier USB 4–8 GHz IF LO LSB Millitech MCA-12-120187 WR-12 Y junction power splitter Test Bench Setup Image Rejection Performance for Each Mixer Pair Millitech MCA-12120187 Balanced Mixers IF = 6 GHz 35 30 19-1/19-3, LSB 25 19-1/19-3, USB 19-1/20-2, LSB 19-1/20-2, USB 20 IR (dB) 19-1/20-4, LSB 19-1/20-4, USB 15 19-3/20-4, LSB 19-3/20-4, USB 20-2/19-3, LSB 10 20-2/19-3, USB 20-2/20-4, LSB 5 20-2/20-4, USB 0 60 65 70 75 80 RF (GHz) 85 90 95 Pairs Used on Inserts IF = 6 GHz 35 30 25 20 IR (dB) 19-1/19-3, LSB 19-1/19-3, USB 15 20-2/20-4, LSB 20-2/20-4, USB 10 5 0 60 65 70 75 80 RF (GHz) 85 90 95 } MMIC } MIC Complete E-band Downconverter Assy. Receiver Testing in Lab Receiver Temperatures at the Telescope* Frequency: 72.8 GHz, LSB, 1st IF = 5 GHz SIS (1) MIC SIS(2) MMIC 64 56 64 78 68 (USB) 60 (USB) *Noise temperature measured with Y-factor method, using hot / cold loads at the window of each receiver. Observations: SIS / MIC SIS Object: IRC+10216 Frequency: 72.8 GHz Integration time: 10hrs, 42min Tsys: 403 K (SIS), 303 (MIC), Trec = 64 K (SIS), 56 K (MIC) MIC Observations: SIS / MMIC SIS Object: IRC+10216 Frequency: 72.8 GHz Integration time: 10hrs, 42min Tsys: 264 K (SIS), 333 (MIC), Trec: 64 K (SIS), 78 (MMIC) MMIC Conclusions • Amplifier technology has shown comparable noise performance as compared to SIS mixer technology which has been the benchmark for the state-of-the-art over the past 20+ years. • Use of cooled amplifiers reduces the number of cooled components and complexity of the receiver dewar. • Increase reliability • Moves image separating mixer outside the dewar • 1/f stability may still be an issue: • Increases with the number of stages in an amplifier • Typically worse in amplifiers, especially when gate widths become shorter • Important for continuum observations but may not be as much as an issue for spectral line work since a narrower bandwidth is utilized • E-band downconverter needs improvement to meet the ALMA spec. of better than 10 dB of IR, further improvement is needed for singledish observations.