Focal Plane Receiver Architecture for ASTE and Total Power Array of ALMA. Jung-Won Lee

Transcription

1 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

2 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

3 ASTE 10m antenna

4 ASTE 10m antenna: site (Matsuhita+1999) (Takekoshi+2012)

5 ASTE Antenna Geometry I

6 ASTE Geometry II

7 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

8 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, GHz à consistent with 7.5 arcmin^2 FOV (Takekoshi+2012)

9 Focal Plane Array: total size total size of array: cryostat window, sideband separation, polarizer etc.

10 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

11 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.

12 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 (B7-10) 17 W mm for 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) (Sugimoto+2009)

13 Wide-IF GHz SIS mixer (under development) side beam lead (4um THK) probe distributed SIS juncti on array 3um-THK si RF choke (LPF filter) licon substr ate IF beam lead instantaneous IF BW :~ 30 GHz supported by distributed junction array architecture suitable for array applications

14 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)

15 Baik (2014) s presentation

16 Baik (2014) s presentation

17 Ke Wu s presenta

18 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)

19 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

20 Focal Plane Array for TP array: p arametric amplifier Shan(2014) s presentation

21 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

22 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

23 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 : 2 nd quarter of 2014 Proof of concept: 2015 receiver construction expected during