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

MMIC

MIC

Receiver Architecture

Amplifier

SIS Mixer IF Amplifier

1.5 GHz IF to Backends

E-band downconverter

Dewar Boundary

4-8 GHz 1st IF

1.5 GHz 2nd IF downconverter

1.5 GHz IF to Backends

LSB

USB

SISLO

SB selector switch

• SIS mixer channel operates in single-sideband mode

• Amplifier channel utilizes sideband-separating mode

LO

Needed for MMIC

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 couplerMillitech

MCA-12-120187

MillitechMCA-12-120187

MAC Tech.C7256 4-12 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

60 65 70 75 80 85 90 950

5

10

15

20

25

30

35

IF = 6 GHz

19-1/19-3, LSB19-1/19-3, USB19-1/20-2, LSB19-1/20-2, USB19-1/20-4, LSB19-1/20-4, USB19-3/20-4, LSB19-3/20-4, USB20-2/19-3, LSB20-2/19-3, USB20-2/20-4, LSB20-2/20-4, USB

RF (GHz)

IR (d

B)

Millitech MCA-12-120187 Bal-anced Mixers

Pairs Used on Inserts

60 65 70 75 80 85 90 950

5

10

15

20

25

30

35

IF = 6 GHz

19-1/19-3, LSB19-1/19-3, USB20-2/20-4, LSB20-2/20-4, USB

RF (GHz)

IR (d

B) } MMIC

} MIC

Complete E-band Downconverter Assy.

Receiver Testing in Lab

Receiver Temperatures at the Telescope*

SIS (1) MIC SIS(2) MMIC

64 56 64 78

68 (USB) 60 (USB)

Frequency: 72.8 GHz, LSB, 1st IF = 5 GHz

*Noise temperature measured with Y-factor method, using hot / cold loads at the window of each receiver.

Observations: SIS / MICSIS MIC

Object: IRC+10216Frequency: 72.8 GHzIntegration time: 10hrs, 42minTsys: 403 K (SIS), 303 (MIC), Trec = 64 K (SIS), 56 K (MIC)

Observations: SIS / MMICMMIC

Object: IRC+10216Frequency: 72.8 GHzIntegration time: 10hrs, 42minTsys: 264 K (SIS), 333 (MIC), Trec: 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.