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 ~(F​𝜆)↑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/32​𝐹↑3 )(​ℎ/𝑎 )​(​𝑟/𝑎 )↑2 ​−​ℎ/32​𝐹↑3 ​𝑟/𝑎 ↑3 𝑐𝑜𝑠𝜑
•  Point source reflected by subreflector(ds= subreflector-focus distance),
​𝐸↓𝑠𝑢𝑏 ∝​exp​(𝑗𝑘​​𝑟↑2 /2​𝑑↓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)
12 ​𝑊↓0 •  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)
Focal Plane Array: total size
•  total size of array: cryostat window, sideband separation, polarizer etc.
ALMA short spacing+ TP array
compatibility
12m
Iguchi+(2009)
•  12m TP + 12 m array only = 6-15m baseline missing à 7m array
•  sensitivity differenceà generic integration time during mosaicing 1:4:4
Total integration time
Mason+(2013) AL
MA memo 598
•  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)
100mm (B710)
17 ​𝑊↓0 (Sugimoto+2009)
•  115 mm for W0~Fl @345 GHz
•  Petzval radius of curvature~ d*F/D ~ 300 mm
•  Axial displacement= ​(​𝛿↓𝑙 ↑2 )/2​𝑅↓𝑝𝑒𝑡𝑧 ~17mm for 100mm lateral offset
à 1/M^2 subreflector refocusing needed(~1/400, 2.5um/mm)
Wide-IF 220-320 GHz SIS mixer
(under development)
side beam lead
(4um THK)
IF beam lead
probe
3um-THK si
licon substr
ate
distributed SIS juncti
on array
RF choke (LPF filter)
•  instantaneous IF BW :~ 30 GHz
supported by distributed junction array
•  architecture suitable for array applications
Feed horn Array for TP array
•  Increasing mapping speed : # of pixels ~ 9 pixels
•  All components should be of large format.
Stacking: Silicon platelets, Brittona(2010)
Baik (2014)’s presentation
Baik (2014)’s presentation
Ke Wu’s presentation
Focal Plane Array for TP array: b
alanced mixers
•  LO sideband noise can be reduced
•  17dB less LO power than for a single-ended mix
er
•  2X dynamic range
•  No external LO diplexer
IF 180 deg. hybrids
Balanced mixer with the same bia
s polarity(Kerr,2006)
Focal Plane Array for TP array: lo
w power-dissipating LNA
•  Conventional transistor-based LNA(3 stage)~10mW
•  Allowed heat~ 41, 160, 850 mW to 4/15/110 K
•  Novel parametric amplifier under test
Shan(2014)’s presentation
Focal Plane Array for TP array: p
arametric amplifier
Shan(2014)’s presentation
Focal Plane Array for TP array
• 
Kojima(2013)
Design for FPA should be compatible with the current ALMA
specifications – IF bandwidth, polarization/ reimaging optics,
heat load
Focal Plane Array for TP array: c
ompatibility
• 
• 
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 incr
ease coldhead power
Summary
•  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