Focal Plane Receiver Architecture for ASTE

and Total Power Array of ALMA

Jung-Won Lee

Korea Astronomy and Space Science Institute

ASTE-ALMA Development Workshop, June 17, 2014

Focal Plane Array: Sampling considerations

•  Density of efficiency-optimized horn array at focal plane Well coupled beam opening angle ~ D/f à beam solid angle= (D/f)^2 •  From the relation of 𝐴↓𝑒 = 𝜆↑2   / Ω↓𝐴  à 𝐴↓𝑒 ~(F𝜆)↑2  , which means minimum spacing needed is larger than 𝐹𝜆/1.8 taking geometric area of the aperture into account. (note) Nyquist sampling criterion = 1/2 ∗𝜆↑   /𝐷 ∗𝑓= 1/2 𝐹𝜆

ASTE 10m antenna

ASTE 10m antenna: site

(Matsuhita+1999) (Takekoshi+2012)

ASTE Antenna Geometry I

ASTE Geometry II

Focal Plane Array: FOV of ASTE (Ref.) Murphy & Padman (1988), IRMMW •  Aberration function with offset h, subreflector radius a, & magnification M Φ(𝛼,𝑟)≃𝑀( ℎ/32𝐹↑3  )( ℎ/𝑎 ) ( 𝑟/𝑎 )↑2 − ℎ/32𝐹↑3  𝑟/𝑎 ↑3   𝑐𝑜𝑠𝜑 •  Point source reflected by subreflector(ds= subreflector-focus distance), 𝐸↓𝑠𝑢𝑏 ∝exp(𝑗𝑘𝑟↑2 /2𝑑↓𝑠  +Φ(𝛼,𝑟))↑    •  “Array beam” with offset h, assuming Gaussian beam W, •  Coupling efficiency between source response and the array beams

(note) assuming 10 dB edge taper spillover

curvature

Focal Plane Array: FOV of ASTE •  ASTE antenna parameters 2a= 620 mm, F=f/D=8.8 (8?), M=22.86, wavelength~ 0.87 (345 GHz)

•  Corrugated feed horn aperture ~ 3 W_0; for good efficiency W_0 ∝Fl •  64 beams are possible assuming corr. horn array on square grid •  From plate scale, 12W_0 corresponds to 3.6 arcmin at 345 GHz, 2.7 arcmin @ 460 GHz à consistent with 7.5 arcmin^2 FOV (Takekoshi+2012)

12 𝑊↓0 

Focal Plane Array: total size

•  total size of array: cryostat window, sideband separation, polarizer etc.

12m

•  12m TP + 12 m array only = 6-15m baseline missing à 7m array •  sensitivity differenceà generic integration time during mosaicing 1:4:4

ALMA short spacing+ TP array

compatibility

Iguchi+(2009)

Mason+(2013) ALMA memo 598

Total integration time

•  Jy/beam noise of SD map = noise of synthesis map to be combined •  having 8 pixels can provide advantage in mapping speed of SD array.

Focal Plane Array: FOV of ALMA 12m •  ALMA 12m antenna parameters 2a= 750 mm, F=f/D=8 , M=20, wavelength~ 0.87 (345 GHz)

•  115 mm for W0~Fl @345 GHz •  Petzval radius of curvature~ d*F/D ~ 300 mm •  Axial displacement= ( 𝛿↓𝑙 ↑2   )/2𝑅↓𝑝𝑒𝑡𝑧    ~17mm for 100mm lateral offset à 1/M^2 subreflector refocusing needed(~1/400, 2.5um/mm)

17 𝑊↓0 

(Sugimoto+2009)

100mm (B7-10)

probe distributed SIS junction array RF choke (LPF filter)

IF beam lead

side beam lead (4um THK)

3um-THK silicon substrate

Wide-IF 220-320 GHz SIS mixer (under development)

•  instantaneous IF BW :~ 30 GHz supported by distributed junction array •  architecture suitable for array applications

•  Increasing mapping speed : # of pixels ~ 9 pixels •  All components should be of large format.

Feed horn Array for TP array

Stacking: Silicon platelets, Brittona(2010)

Baik (2014)’s presentation

Baik (2014)’s presentation

Ke Wu’s presentation

•  LO sideband noise can be reduced •  17dB less LO power than for a single-ended mix

er •  2X dynamic range •  No external LO diplexer

Focal Plane Array for TP array: balanced mixers

Balanced mixer with the same bias polarity(Kerr,2006)

IF 180 deg. hybrids

•  Conventional transistor-based LNA(3 stage)~10mW •  Allowed heat~ 41, 160, 850 mW to 4/15/110 K •  Novel parametric amplifier under test

Focal Plane Array for TP array: low power-dissipating LNA

Shan(2014)’s presentation

Focal Plane Array for TP array: parametric amplifier Shan(2014)’s presentation

Focal Plane Array for TP array

•  Design for FPA should be compatible with the current ALMA specifications – IF bandwidth, polarization/ reimaging optics, heat load

Kojima(2013)

•  Allowed heat~ 41, 160, 850 mW to 4/15/110 K •  Heat load calculation based on Kojima’s estimate(2013, last workshop) 4K : depends on configurations of each band(2SB ..) SST LO waveguide run (0.4 mW) Wiring (3.1 mW) IF coax(1.4 mW) IF LNA(8mW X 4) à ~1mW, 30dB gain LNA (4-8 GHz) by Chalmers ------------------------- subtotal: 37 mW If we assume 9 beam à (5mW*9 = 45 mW, 4mW*9= 36 mW) : need to increase coldhead power

Focal Plane Array for TP array: compatibility

•  9 beams for ALMA TP array is preferred (coldhead power needs to be improved.) •  64 beams are possible with ASTE focal plane. •  Integration (RF hybrid, IF hybrid) approaches to be demonstrated. •  All RF/IF spec same as ALMA band(exception polarizer) •  Initial feasibility study on 345 GHz or 460 GHz receiver a

rchitecture : 2nd quarter of 2014 •  Proof of concept: 2015 •  receiver construction expected during 2016-2017

Summary