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27 August 200827 August 2008 CMBPol Technology WorkshopCMBPol Technology Workshop 11
Adding Interferometryfor CMBPol
Peter Timbie University of Wisconsin - Madison
QuickTime™ and aTIFF (Uncompressed) decompressor
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27 August 2008 CMBPol Technology Workshop 2
Imaging and Interferometry
FT
Visibilites V(u,v)
FTCl
l
correlator
Cl
l
27 August 2008 CMBPol Technology Workshop 3
OutlineWhy interferometry?ChallengesBeam combination: pairwise vs ‘all-on-one’, multiplying vs addingGuided-wave beam combinerQuasi-optical beam combiner
MBIEPIC Interferometer
Required technologies (bolometric interferometer)horn antenna arraysOMTsphase modulatorsbeam combiner/correlatorfiltersbolometers/readout100 mK cooler
Discussion
27 August 2008 CMBPol Technology Workshop 4
CMB Interferometers
HEMT810’, 3’30, 90SZA
ν (GHz) FOV # ant’s receivers
DASI 30 5o 13 HEMTCBI 30 44’ 13 HEMTMINT 150 30’ 4 SIS
VSA 30 7o 14 HEMTBIMA 30 6’ 6 HEMTOVRO 30 4’ 9 HEMTT-W 45 5o 2 SISBAM 90-270 42’ 2 BoloVLA 5, 8, 16 7’ 27 HEMT
Interferometers for the CMB
27 August 2008 CMBPol Technology Workshop 5
Why CMB Interferometry? Systematics!• simple optics
- forms beams with corrugated horn arrays
- symmetric beam patterns, low sidelobes, no mirrors
• no off-axis aberrations
• Stokes U measured by correlation of Ex and Ey on a single detector(no differencing of detectors)
• differences sky signals without scanning
• measures power spectrum directly
• measures both Temp and Polarization anisotropy
• coherent (HEMTs) or incoherent (bolometers) systems possible
• angular resolution ~ 2X better than imager of equivalent diameter
• CMB polarization first detected with interferometer (DASI)
• simple scan strategy - rotate about optical axis, move on to new pixel
27 August 2008 CMBPol Technology Workshop 6
Interferometer beam systematics: example
j
n1 n2
uij
VijU = dn1∫ dn2Gix (n1 )G jy (n2 ) Eix (n1 )E jy (n2 )
i
= dn∫ Gix (n)G jy (n)U(n)ei2πuij ⋅n
U(n1 )e2πiuij ⋅n1 δ(n1 − n2 )
So - beam mismatch, distortion, etc. do not couple T intoStokes U visibility measurement.
y
x
X
27 August 2008 CMBPol Technology Workshop 7
Challenges for Interferometry
• beam combiner - scalable, low loss
• “fringe smearing” from wide bandwidths
• simulations
27 August 2008 CMBPol Technology Workshop 8
Beam Combination1. Pairwise (Michelson): signals are split and combined pairwise
• N(N-1)/2 pairs (78 for N = 13, 4950 for N =100)
• multiplying correlator (coherent receivers only)a. analog (DASI/CBI)b. digital (most radio interferometers)
see Coherent Detectors, C. Lawrence et al.- power?- bandwidth?
• adding correlator with bolometers: M. Hattori, Tohoku University
2. Fizeau (Butler): signals from all antennas appear at all detectors
• Fizeau approach has lower noise in background-limited case, in low n limit(Zmuidzinas 2003)
• Hamilton et al. (astro-ph/0807.0438) compares to imaging
• Guided-wave adding interferometer (Butler combiner, Rotman lens)
• Quasioptical adding interferometer using a telescope (MBI)
27 August 2008 CMBPol Technology Workshop 9
Ryle’s Adding Interferometer (1952)
“visibility”
10
Adding interferometer for N > 2
OMTs
1||1 EE +⊥ 2||2 EE +⊥
N
EEEE
N
EEEE NNNN∗
⊥⊥⊥⊥ +++×
+++ )...()...( ||1||1||1||1
=(E⊥1
2 + ...E⊥N2 ) + (E⊥1E||1 + ...E⊥N E||N ) + (E⊥1E||2 + ...E⊥1E||N ) + (E⊥1E⊥2 + ...E||E||N )
N
total power single-hornauto-correlation
Stokes Uvisibilities
N horns
2N phase modulators
beam combiner
detectors
E⊥N + E||N
Stokes Ivisibilities
⊥// ⊥// ⊥//….
….
27 August 2008 CMBPol Technology Workshop 11
I. Guided-wave beam combiner
• Waveguides or planar transmission line• Butler combiners (N inputs and N outputs)• Rotman lens (N inputs, > N outputs)• Losses may restrict to coherent receivers (with gain)
27 August 2008 CMBPol Technology Workshop 12
φ
φ
φ
φ
T Q U
Geometricdelays
φ
φ
φ
φ
φφRotman Lens stack
Phaseswitches
Dio
de D
etec
tor a
rray
Anti-reflection resistive layer
2D horn array
Orthogonal cross stack
OMTs
Idealised Rotman interferometer scheme showing the input TQU maps and the paths through to the detectors. The signal from each sky element reaches each horn with different geometric delays. OMTs split the signals into different hands of polarization which are then phase switched independently before being input to the first Rotman stack. The column followed by the row stack performs a Fourier transform and the Fourier transform of these detected outputs gives the visibility information.
Rotman Lens interferometer scheme(see poster by R.A. Watson & L. Piccirillo)
Dio
de d
etec
tor a
rray
(HEMTs)
27 August 2008 CMBPol Technology Workshop 13
A B C D
Antenna ports
Beam ports
Dummy ports
Dum
my p
orts
Dummy ports
Dummy ports
-7 /8π
-7 /8π
-7 /16π-7 /16π
-5 /16π-5 /16π-3 /16π
-3 /16π- /16π- /16ππ/16
π/163 /16π
3 /16π
5 /16π5 /16π
7 /16π7 /16π -5 /8π
-5 /8π-3 /8π
-3 /8π
- /8π
- /8π
π/8
π/8
3π/8
3π/8
5π/8
5π/8
7 /8π
7 /8π
The Rotman Lens: Alternative to Butler combiner(Watson & Piccirillo)
HFSS simulation of a Rotman Lens. The relative phase on the outputs is given in different colours for each antenna port.
Rotman lens (Rotman and Turner 1963) is a planar transmission line implementation of the quasi-optical combiner.
It consists of a set of beam and antenna ports either side of a specially shaped parallel plate cavity through which the waves propagate.
The design is simple and many inputs and outputs can be easily incorporated, unlike a Butler combiner
It can be implemented cheaply in microstrip and using high dielectric constant substrate (εr>10) can reduce size sqrt(εr) (>3).
27 August 2008 CMBPol Technology Workshop 14
II. Adding interferometer with a quasi-optical beam combiner
• Millimeter-wave Bolometric Interferometer (MBI)• EPIC Interferometer
27 August 2008 CMBPol Technology Workshop 15
Bolometer Array
Parabolic mirror
Phase Shifters
Feed horn antennasCryostat
45° CW twist rectangular wave guide
45º CCW twist rectangular wave guide
Quasioptical Beam Combiner
27 August 2008 CMBPol Technology Workshop 16
The Millimeter-Wave Bolometric Interferometer (MBI)
• Fizeau (optical) beam combiner
• 4 feedhorns (6 baselines)
• 90 GHz (3 mm)
• ~1o angular resolution
• 7o FOV
Antennas
Liquid nitrogen tank
Liquid helium tank
Secondary mirror
3He refrigerator
Primary mirror
Bolometer unit
Phase modulators
27 August 2008 CMBPol Technology Workshop 17
Effect of Phase Shifting
Single Baseline
(Two feeds)
Six baselines
(Four feeds)
27 August 2008 CMBPol Technology Workshop 18
MBI Assembly
19 spider-web bolos (JPL)
15 cm
27 August 2008 CMBPol Technology Workshop 19
MBI Team
Lucio PiccirilloUniversity of Manchester
Evan Bierman, Brian KeatingUC San Diego
Peter Timbie, Amanda Gault Peter Hyland, Siddharth Malu
University of Wisconsin - Madison
Ben WandeltUniversity of Illinois
Creidhe O’Sullivan, Gareth CurranNational University of Ireland - Maynooth
Peter Ade, Carolina CalderonCardiff University
Ted BunnUniversity of Richmond
Greg Tucker, Andrei Korotkov Jaiseung Kim
Brown University
27 August 2008 CMBPol Technology Workshop 20
First lightat
Pine Bluff ObservatoryMadison, WIMarch 2008
27 August 2008 CMBPol Technology Workshop 21
MBI interference fringes
Tucker et al. SPIE 2008
22
Einstein Polarization Interferometer for Cosmology (EPIC) Mission Concept
Backshort Under Grid (BUG)TES array (NASA/GSFC)
64-element module(1 of 16)
25 cm at λ = 0.3 cm
Interference fringes measured infocal plane by bolometer array
RF phase modulators
Corrugated horns
Fizeau beam combiner
OMTs
23
EPIC LEO Mission Concept
1.75 m dia
90 GHz module(1 of 8) 0.25 m dia
60 GHz
30 GHz
150 GHz
250 GHz
0.9 m
27 August 2008 CMBPol Technology Workshop 24
• Measure CMB E and B mode polarization over full sky toforeground limit (T/S ~ 0.01)
Scaled close-packed corrugated horn arrays: 30-300 GHz
~15o FOV, ~ 1o synthesized beams
Total # horns N ~ 1024 (= # modes) x 2 pol’ns
Interferometer: signals cross-correlated
- between horns: N(N-1)/2 visibilities for small scales
- between 2 polarizations for each horn: “correlation polarimetry” for large scales
Lifetime > 1yr from 900 km Earth orbit (COBE)
EPIC LEO Mission Concept
LHe Dewar
Spacecraft Bus
Arrays
27 August 2008 CMBPol Technology Workshop 25
EPIC sensitivity calculation
• each array module has N = 64 antennas, 2 polarizations• signal from each antenna spread out over focal plane of
4N = 256 detectors• phase-modulated fringe signal meas’d independently
by each detector• background-limited detectors in focal plane of beam combiner• η = 0.5, 20 % BW• 4N demodulated signals are then added in quadrature
to compute visibility• repeat for each of the 2N(2N-2)/2 visibilities (all baselines)• add in quadrature signals from other arrays at 90 GHz• 1 - year integration over full sky (“Knox” formula)• see J. C. Hamilton et al. (astro-ph/0807.0438)• - comparison with imager, coherent interferometer
- simulation
27 August 2008 CMBPol Technology Workshop 26
EPIC Sensitivity
27 August 2008 CMBPol Technology Workshop 27
Interferometer “Fringe Smearing”
• 1-D simulation
• diffuse source(CMB) with flatpower spectrum
• horn apertureD ~ 17λ
~7° FWHM beam
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spacing
D2D4D6D8D 12D 16D
27 August 2008 CMBPol Technology Workshop 28
Horn Antenna Arrays
• need close-packed arrays of ~ 8 x 8 antennasfrom 30 GHz to 300 GHz
• total of 1024 horns for EPIC Interferometer
• platelet arrays (see Gundersen and Wollack)
• smooth-walled horns (Yassin et al.)
29
G. Yassin
Easy machining!
30
27 August 2008 CMBPol Technology Workshop 31
Ortho-mode transducers
• separate X/Y linear or R/L circular polarization modes
• input: interface to circular horn output
• output: interface to phase modulator (waveguide or transmission line)
• low-loss (< 0.5 dB)
• low cross-coupling (< - 40 dB?)
• bandwidth ~ 30%
• mass production? 1024 required, bands from 30 GHz - 300 GHz
• see ClOVER design, Giampaolo Pisano et al.
27 August 2008 CMBPol Technology Workshop 32
CIOVER OMT
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• G. Pisano et al.IEEE Micr. and Wireless Comp. Lett.17(4) 2007
• electroformed copper
• WR10 waveguide band (75-110 GHz)
• ms’d return loss -22 dB avg. across band
• ms’d isolation -45 dB avg. across band
• 100’s req’d for ClOVER
27 August 2008 CMBPol Technology Workshop 33
Phase Modulators• require 2 for each antenna (one per polarization)• input interfaces to OMT output (w’guide or transmission line)• ~ 30% bandwidth• low insertion loss (< 0.5 dB)• low amplitude modulation• step through a phase sequence similar to Walsh function
- co-add signals from redundant baselines (Charlassier et al. ‘08)- # steps minimized by having multiple phase angles
(Hyland, Follin, & Bunn arXiv:0808.2403v1)• for 8 x 8 array
- steps of 360/15 = 24° is optimal- sequence length is 675 steps
• switching speed > 100 Hz• waveguide Ferrite Rotation Modulator (FRM) see B. Keating• planar modulators (MEMs and SIS) see A. Kogut
27 August 2008 CMBPol Technology Workshop 34
Ferrite phase shifter performance
Gault, Malu, Bierman, Keating, et al.
27 August 2008 CMBPol Technology Workshop 35
Bolometers
• filled arrays required to capture all radiation in focal plane• # pixels ~ 4 X Nhorns for each interferometer module• near photon noise limit for
-optical efficiency of ~ 12% ( ~ 50% / 4)-bandwidth 30%-CMB background loading
• Backshort Under Grid (BUG) arrays for GISMO (λ = 2 mm)- increase 64 pixels → 256 pixels- reduce G- extend to λ = 1 cm- $400K/yr for 3 years
• other candidates?
27 August 2008 CMBPol Technology Workshop 36
Adding Interferometer Systems
Complete systems are required to test the conceptMBI-4 ….MBI/BRAIN
Simulations have just become available this year:R.A. Watson & L. Piccirillo (poster)J.-C. Hamilton et al. (2008) ArXiv 0807.0438
37
PSD1 VL-HR PSD2 VL-VRPSD3 HL-VL PSD4 HL-VRPSD5 HL-HRPSD6 HR-VR
Initial simple simulations of Rotman interferometer (Watson & Piccirillo)
The simulation was carried on a 4x4 array shown in figure 4 with a 5o FWHM with a spacing of 20 wavelengths between elements using a HEALpix TQU map generated by synfast using a concordance model.
The signal from each HEALpix pixel is traced through all horns through the Rotman stacks to the detectors where the complex sum is made and its contribution detector power determined
The lower panels show the real and imaginary parts of visibilies recovered by the FFT on the different phase switched detector stacks.
The stronger unpolarized signals (CMB fluctuations) can be seen on PSD channels 2, 5 and 7 with weaker polarized U visibilities at 10% on PSDs 1,3,4 and 6
TQU HEALpix map
Geometry of dual polarization elements
Correlation pairs for each PSD lock-in
38
BRAIN/MBI
First module fordeployment at Dome C,Antarctica
Workshop at APC, Paris, June ‘08 “Bolometric Interferometry for the B-mode Search” Bolometer arrayBolometer array
phase phase shifteshifte
rsrs
hornshorns
backbackhornshorns
30 K
300 mK
30 K
30 K
Sky
70 cm
60 cm
10 cm
10 cm
40 cm
•United States•Brown University•University of Wisconsin, Madison•University of Richmond•UC San Diego•University of Illinois
•United Kingdom•University of Wales, Cardiff•University of Manchester•NUI Maynooth
•France–Astroparticule et Cosmologie (APC), Paris–Centre d’Étude Spatiale de Rayonnements (CESR), Toulouse–Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM), Orsay–Institut d’Astrophysique Spatiale (IAS), Orsay
•Italy–Università di Milano - Bicocca–Università di Roma - La Sapienza
•United Kingdom–University of Manchester–University of Wales - Cardiff
Bolometric Radiation INterferometer MBI
27 August 2008 CMBPol Technology Workshop 39
Adding Interferometer Technology Readiness
Planck & HerschelGISMO
86
focal plane bolometer arrays - NTD Ge- Backshort-Under-Grid TES
BICEP & MBIPAPPA
52/3
phase modulator- ferrite (2 state, <150 GHz)- MEMs/SIS (2 state)
MBITBD
52
beam combiner- quasi-optical- guided-wave
ASTRO-E29Sub-K Cooler: Single-shot ADRSpitzer, ISO, Herschel, COBE9LHe Cryostat
WMAPClOVER
94/5
OMT (< 100 GHz)ClOVER OMT (150 GHz?)
WMAP & COBEQUIETTBD
953
corrugated horn antennas (singles)platelet arrayssmooth-wall horn arrays
HeritageTRLTechnology
27 August 2008 CMBPol Technology Workshop 40
SummaryWhy interferometry?ChallengesBeam combination: pairwise vs ‘all-on-one’Guided-wave beam combinerQuasi-optical beam combiner
MBIEPIC Interferometer
Required technologies (bolometric interferometer)horn antenna arraysOMTsphase modulatorsbeam combiner/correlatorfiltersbolometers/readout100 mK cooler
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