SIS mixers for 1mm band A. Navarrini, G. Engargiola, R. Plambeck (Berkeley) N. Wadefalk (Caltech)

1. SIS mixers for 1mm bandA. Navarrini, G. Engargiola, R. Plambeck (Berkeley)N. Wadefalk (Caltech) • short term: increase bandwidth of existing BIMA mixers to 4 GHz • long term: develop new generation of 1mm mixers using UVa SIS mixers

2. Current BIMA 1mm receivers • DSB, fixed-tuned SIS mixers • single SIS junction devices fabricated by G. Engargiola at U. Illinois • 800 MHz IF band, 1.4 - 2.2 GHz (limited by IF amp)

3. DSB receiver temperatures ~ 50 to 80 K(measured outside dewar, including all optics losses) 5.5 K 4.5 K 3.6 K

4. Need to replace narrowband IF amplifier • ALMA solution is to build I.F. amplifier from discrete transistors • more flexibility in matching impedance of SIS junction • our preferred solution is to use InP MMIC • WBA13, developed by Weinreb and Wadefalk for ATA • 35 dB gain, noise temp 3-6 K • 10-20 mW power dissipation

5. Comparison of amplifier gains, noise temperatures ALMA Band 6 amplifier, designed for 4-12 GHz WBA13 MMIC, designed for 0.5-11.5 GHz Gene Lauria, ALMA Band 6 PDR, Apr 2004 Wadefalk and Weinreb

6. Option 1: replace amplifier on 12 K stage with MMIC module (WBA13 amplifier module provided by N. Wadefalk)

7. Option 1: Trcvr DSB measured with 0-6 GHz I.F. filtercomparable to narrowband results

8. Option 1: gain and noise from 0-9 GHzripple tolerable from 225-240 GHz, bad outside this range 225 GHz 260 GHz

9. Option 2: integrate MMIC directly into mixer block • MMIC tended to oscillate; had to switch from WBA13 to lower-gain WBA12 • mixer block at 4.65 K instead of 3.85 K • gain ripple still a problem

10. Option 3: incorporate pre-packaged WBA13 (ATA module) into thermally-split block 12 K 3.8 K

11. Option 3: DSB noise temperatures 0-6 GHz I.F. filter

12. Option 3: gain, noise from 0-6 GHz (ripple much improved, but gain falls off above 3 GHz) 225 GHz 260 GHz

13. broadening bandwidth of BIMA 1mm mixers to 4 GHz: short term solutions if we must have 4 GHz bandwidth by Fall 2005, option 1 probably is best

14. Longer term • goal: DSB Trcvr = 25 K, 8 GHz I.F. bandwidth • switch to ALMA Band 6 devices • we have only ~50 usable UI junctions • NRAO has contracted for 9 UVa wafers, each with 1066 devices (9600 devices); approx 50% are usable • if necessary, we could contract with UVa for an additional wafer • construct thermally split block with WBA13 IF amp • operating WBA13 at 12 K reduces heat load on 4 K refrig, may also improve 1/f gain stability of MMIC

15. ALMA Band 6 SIS devices • DSB Trcvr ~ 20 K • series array of 4 junctions – avoids problems with saturation, but requires more LO pwr Tony Kerr has given us 4 ALMA devices to try

16. ALMA is building sideband separating mixers, but we would use devices as DSB mixers • sideband separation requires complex mixer block, carefully phase-matched preamps • NRAO estimates ~25% acceptance rate for ALMA mixers from ALMA Band 6 PDR, Apr 2004

17. ALMA sideband separating mixer blockwith attached preamps

19. Sensitivity comparisons