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 H 2 CO line at 72.8 GHz

Receiver Architecture SIS MMIC MIC

Receiver Architecture Amplifier SIS Mixer IF Amplifier 1.5 GHz IF to Backends E-band downconverter Dewar Boundary 4-8 GHz 1 st IF 1.5 GHz 2 nd IF downconverter 1.5 GHz IF to Backends LSB USB SIS LO SB selector switch SIS mixer channel operates in single- sideband mode Amplifier channel utilizes sideband- separating mode LO Needed for MMIC

Legacy 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 Millitech MCA Millitech MCA MAC Tech. C GHz quad. hybrid coupler USB LSB Front end signal from amplifier WR-12 Y junction power splitter LO 4 – 8 GHz IF

Test Bench Setup

Image Rejection Performance for Each Mixer Pair

Pairs Used on Inserts } MMIC } MIC

Complete E-band Downconverter Assy.

Receiver Testing in Lab

Receiver Temperatures at the Telescope* SIS (1)MICSIS(2)MMIC (USB) 60 (USB) Frequency: 72.8 GHz, LSB, 1 st IF = 5 GHz *Noise temperature measured with Y-factor method, using hot / cold loads at the window of each receiver.

Observations: SIS / MIC SISMIC Object: IRC Frequency: 72.8 GHz Integration time: 10hrs, 42min Tsys: 403 K (SIS), 303 (MIC), T rec = 64 K (SIS), 56 K (MIC)

Observations: SIS / MMIC MMIC Object: IRC Frequency: 72.8 GHz Integration time: 10hrs, 42min T sys : 264 K (SIS), 333 (MIC), T rec : 64 K (SIS), 78 (MMIC) SIS

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 single- dish observations.