A Q-band 19 pixel multifeed receiver for the Sardinia Radio Telescope
ALESSANDRO ORFEI, INAF-IRA National Institute for Astrophysics – Institute of Radioastronomy
Radionet Online Workshop Bonn, September 21-22 ,2020 1
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SARDINIA RADIO TELESCOPE (SRT)
• Primary Mirror D=64 m; Secondary Mirror D=7.9 m
• Gregorian Configuration with Shaped Surfaces
• Active Surface: Primary mirror with 1116 actuators
(Shaped Parabolic)
• Six focal positions:
Primary, Gregorian, Four Beam Wave Guide
• Can host up to 20 dual polarization receivers:
mono feed, dual frequency, multibeam
Swapped remotely and automatically
• Primary surface accuracy: 300 m RMS today,
120 m goal
• Max antenna efficiency: 60 %
• Pointing accuracy (RMS): 5 arcsec,
2 arcsec goal
• Aim 0.3-116 GHz frequency coverage
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INTRODUCTION
THE AIM for a Q-band MULTIFEED STARTED LONG TIME AGO
PHASE 1, 2009-june12 PROVING TECHNOLOGIES (FP7 JOINT RESEARCH ACTIVITY,
EU-RADIONET FUNDS) PHASE 2, 2012-2015 DESIGN/CONSTRUCTION of PASSIVE PARTS (ITALIAN FUNDS) PHASE 3, 2016-june19 DESIGN and PROTOTYPE of ACTIVE PARTS (ITALIAN FUNDS) PHASE 4, june19-2021 FINALIZING the PROJECT (ITALIAN FUNDS)
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PROVING TECHNOLOGIES: PASSIVE DEVICES
CORRUGATED HORN & OMT: USE OF PLATELET TECHNIQUE (lower cost)
POLARIZER: Pancharatnam theory
(U. Manchester in collaboration with INAF-IRA, G. PISANO)
OMT:Turnstyle junction
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PROVING TECHNOLOGIES: ACTIVE DEVICE
LNA
AMP
x8
RF IF
LO=4GHz
WHEN ENGINEERING AND PROTOTYPING WE WERE NOT ABLE TO OBTAIN USABLE MODULES
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A Q-band MULTIFEED for the SRT 64m DISH: GOALS
1. SCIENCE: IMAGING for SPECTROSCOPY + FULL STOKES and QUIET SUN (requirement of last years)
2. RF BAND: 33-50 GHz 3. NUMBER of PIXELS: 19, HEXAGONAL CONFIGURATION 4. POLARISATION: CIRCULAR LEFT and RIGHT 5. RF BAND AVAILABLE: 8 BASEBANDS 2GHz WIDE EACH 6. MECHANICAL ROTATOR for EARTH ROTATION COMPENSATION 7. RECEIVER NOISE TEMPERATURE < 30K 8. FIRST SIDE LOBE LEVEL ≤ -20dB 9. POLARISATION PURITY ≥ 30dB 10. NOISE MARKER VARIATION: 1dB THROUGH RF BAND 11. MAINTAINING LINEARITY UP TO QUIET SUN INPUT POWER
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PHASE 2: 2012-2015 (ITALIAN FUNDS)
1. DESIGN of NOISE MARKER INJECTION DEVICE (MJ) 2. REFINE OMT and POLARIZER DESIGN 3. CONSTRUCTION of the 19 HORN/MJ/POLARIZER/OMT CHAINS 4. BUY 19 NOISE GENERATOR 5. MEASURE 19 FEED SYSTEM CHAINS
HORNs POLARIZERs OMTs
MJ NOISE SOURCES MJ
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MEASUREMENTS OF THE PASSIVE PARTS: HORNs
E/H-plane 33GHz, 19 horn E/H-plane 41.5GHz, 19 horn E/H-plane 50GHz, 19 horn
45o-plane 33GHz, 19 horn 45o-plane 41.5GHz, 19 horn 45o-plane 50GHz, 19 horn
collaboration with U. Milano (C. FRANCESCHET)
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MEASUREMENTS OF THE PASSIVE PARTS: HORNs
MULTIHORN; B = 33-50 GHz; BW = 41%
Obtained
33 GHz 41.5 GHz 50 GHz
SIMULATED
Edge taper (dB) -6.2 -10.6 -18.1
Simulated Antenna Gain (K/Jy) 0.62 0.66 0.56
HPBW (arcsec) 32 27 24
Beam Separation (arcsec) 85
MEASURED
S11 (dB) ≤-30 ≤-30 ≤-30
Crosspolarisation (dB) ≤-28.9 ≤-32.8 ≤-30.9
SideLobeLevel (dB) -22 -21 -19
Horn/Horn Isolation (dB) ≤-60 ≤-60 ≤-60
Insertion loss (dB) 0.1 0.1 0.1
MADE BY INAF- ARCETRI OBSERVATORY
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MEASUREMENTS OF THE PASSIVE PARTS: MARKER INJECTOR (MJ)
MEASURED ON 19 DEVICES
MANUFACTURED
S11, S22 circular ports < -35dB
S21 circular ports < 0.08dB
Crosspol circular ports < -50 dB
Coupling vs frequency -20.2 dB ± 0.75 dB
Crosspol rectangular port < -56 dB
NOISE MARKER VARIATION: EACH INDIVIDUAL CURVE WITHIN ±0.5 dB
collaboration with CNR - IEIIT (TORINO)
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MEASUREMENTS OF THE PASSIVE PARTS: POLARIZERs
MAX Ø UNBALANCE (18 over 19 devices): 3 degree (cross= -31.6dB) WORST CASE: 5 degree (cross= -27.2dB)
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MEASUREMENTS OF THE PASSIVE PARTS: OMTs
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MEASUREMENTS OF THE PASSIVE PARTS: 19 FEED SYSTEM
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MEASUREMENTS OF THE PASSIVE PARTS: ATTENUATOR
1. WAVEGUIDE 2. COOLED AT CRYO TEMPERATURE 3. MULTI-HOLE STYLE (directional coupler) 4. NON-FLAT TO COMPENSATE for the DECREASE of NOISE SOURCE ENR vs F 5. FIXED WAVEGUIDE with REMOVABLE DRILLED METAL SHEET
Measured Calculated Interpolation
RF
ALL WAVEGUIDE NOISE MARKER CIRCUIT
NS ATTENUATOR
MJ
Thermal
gap
CRYO WARM
Wg
RF+NOISE
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PHASE 3: 2016-june2019 (ITALIAN FUNDS)
1. PROVIDE A CONVENIENT CRYOGENIC LNA 2. DESIGN of A NEW 1st DOWN CONVERSION MODULE (Q-CONV) 3. DESIGN/CONSTRUCTION of LO DISTRIBUTOR 4. DESIGN of THERMAL GAP 5. DESIGN of FBCB (Full Band Conversion/Continuum Board/Back-end)
20K WARM STAGE
Horn
MJ
Pol
Omt
ATTENUATOR NS
Qconv
Th
erm
al G
ap
Qconv
FBCB
RCP
LCP
LO Distribution RFoF20
TX RX
wguide
33 50
1 18
1 18
ANTENNA DATA CENTER 600m AWAY
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ACTIVE PARTS: LNA
COMMERCIAL DEVICE by LOW NOISE FACTORY (Sweden) - 3 wires only for bias (save hundred of thin wires!) - very low power consumption, 10mW - very good S11, S22, Gain, Noise performance - low P1dB (-12dBm) but sufficient for quiet Sun
MONITORING&CONTROL SYSTEM (INAF)
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ACTIVE PARTS: Q-CONV IN-HOUSE DESIGN of a DOWN CONVERSION MODULE
- MMIC chip DIDN’T WORK - NEW CONVERTER USING MMIC COMMERCIAL DEVICES
WG probe Image
Filter Amp
LO Filter
x2
IF Low pass
Filter
OL=16 GHz
Mixer
33 50 1 18
- x2: ANALOG DEVICE - MIXER: MARKI - AMPLIFIER: CUSTOM MMIC
IN-HOUSE DESIGN: - OL and IF FILTERS on 127m TEFLON SUBSTRATE - WG PROBE and IMAGE FILTER on 127m ALUMINA
SUBSTRATE
53 44
8
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Q-CONV MEASURES
Power consumption = 0.6W
FOUND !
Image rejection ≥ 27dB
NOISE
GAIN
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LO DISTRIBUTOR
1. DISTRIBUTE 38x16GHz LO SIGNALS 2. IN-HOUSE DESIGN 3. 8 OUTPUT ACTIVE SPLITTERS ON PCB 4. 3 LAYERS PCB. STRIPLINE ON RG4003 SUBSTRATE 5. WORKING FREQUENCY UP TO 20GHz
Power consumption/board 0.6W
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TRIPLE WAVEGUIDE THERMAL GAP
LNA PORTS
MJ ATTENUATOR PORT
20K STAGE WARM STAGE
Attenuator NS
Qconv
Qconv
RCP
LCP
wg
Th
erm
al G
ap
T
he
rma
l G
ap
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1. BOARD: TWO IF INPUT 2-18GHz; 16 BASEBAND OUTPUTS+DETECTION 2. BOARD: AMPLITUDE EQUALIZATION OF THE INPUTs 3. BOARD: FULL STOKES DETECTION EMBEDDED 4. BOARD: 6 LAYERS DOUBLE EUROCARD PCB 5. BOARD: 1000+ COMPONENTS ON ROGERS 4003 508m SUBSTRATE SYSTEM: 19 BOARDS + 2nd LOs GENERATION and DISTRIBUTION
FBCB (Full Band Conversion/Continuum Board/Back-end)
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PHASE 4: june19-2021 (ITALIAN FUNDS)
1. CRYOSTAT + MECHANICAL ROTATOR (same as K-band multifeed) 2. MASS PRODUCTION (LNA, Q-CONV, THERMAL GAP, ATTENUATOR, FBCB) 3. RECEIVER MEASUREMENTS
HR500 or mylar or kapton
Horn
Polariser
OMT
LNA
Q-CONV
LO Distributors
Noise
source
MJ
Attenuator
589
630
65
7
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MECHANICAL ROTATOR (SAME AS K-BAND MFEED)
MAIN SPECIFICATIONS
STROKE (degree) ± 132
SPEED (o/s @3000 rpm) 3.276
ACCELERATION (o/s2) 2.67
MAX OUTPUT TORQUE (Nm) 550
MOTOR VOLTAGE (Vdc) 24
ABSOLUTE ENCODER LINEAR RESOLUTION (mm) 0.01
ABSOLUTE ENCODER ANGULAR RESOLUTION (degree) 0.00168
MIN DISPLACEMENT, ON SKY (arcsec) 0.013
POSITIONING ACCURACY, ON SKY (arcsec) 0.036
K-BAND MULTIFEED
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CALCULATION of the PERFORMANCE
Measured
Simulated
Coax 4m
20K WARM STAGE
Horn
MJ
Pol
Omt
Attenuator NS
Qconv
Th
erm
al G
ap
Qconv
FBCB
RCP
LCP
LO Distribution RFoF20
wguide
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THANK YOU !