1The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
The TWIN-Radiotelescopes
WettzellNext generation VLBI-technique
G. Kronschnabl, BKG; Dr. A. Neidhardt, TUM; Dr. K. Pausch, Vertex GmbH; W. Göldi, Mirad; B. Petrachenko, NRCan; A. Emrich, Omnisys;
2The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Radioteleskop Wettzell
RTW: D=20m, S/X-Band; Velocities: 3°& 1.5°/s; Tsys=40K; 1Gbps;
3The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Broadband Delay: VLBI-Working-Scheme
Data-Acqusition-System
Data-Acquisition-System
MW-Receiver
MixerLocal
Oscillator
Frequency-standard
Station-Clock
Formatter
Recorder
Radio source
Station 2
Station 1
t1
Correlator
Delayτobs
t1t2
b
Delay τobs
k
t2 τg=-b.k /c
Quelle: Dr. W. Schwegmann, Dr. A. Neidhardt; VLBI in near-realtime
Scheme of VLBI
4The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
VLBI 2010
VLBI 2010
IVS WG 3 – VLBI2010: Current and future requirements for geodetic VLBI Systems
• Determination of the relative position better than 1 mm / year
• Continuous observation of the Earth Orientation Parameters
• Very fast generation and distribution of the IVS-Products
� continuous, improved UT1 monitoring
� Improving of the Celestial Reference Frame (CRF)
Goals for a next generation VLBI-System:
Source: IVS WG3 Final Report - ftp://ivscc.gsfc.nasa.gov/pub/annual-reports/2005/pdf/spcl-vlbi2010.pdf
5The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Accuracy of the Delay Observable
2
122
1
fSNR
r
π
σ =
where:
SNR = Signal-Noise Ratio
f = VLBI Processing Faktor (ca. 0.55 for 1bit Data streams)
S = Source-Flux (Jy)
Di = Antenna diameter per Station
k = Boltzmannkonstante
ei = Beam efficiency of the antenna
BR = Bitrate
t = Integration time
Tsys = System temperature per station (at the same frequency)
� higher bandwidth
� higher quantization of the signals
� higher effective antenna area
� higher data acquisition rate
� reducing the system temperature
21
2121
26
8
10f
SysSys TT
tBRee
k
DDSSNR
⋅
⋅⋅⋅⋅
⋅
⋅⋅⋅⋅⋅=
−π
Source: IVS WG3 Final Report
6The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
VLBI 2010: Broadband Delay
0
5
10
15
20
25
30
0 2 4 6 8
0
0.5
1
1.5
2
2.5
2 3 4 5 6 70 2 4 6 8 10 12 14 16
Broadband-Sequence with 4 Bands
and a band width of 1 GHz
Phas
e P
has
e
frequency (GHz)
frequency (GHz)
0 2 4 6 8 10 12 14 16
SN
R t
o r
esolv
eth
eP
has
e
No. of frequency bands
No. of frequency bands
Phas
e D
elay
Prä
zisi
on
Standard S/X – Bands with a
band width of 250 & 720 MHz
BW=1 GHz
BW=0.5 GHz
BW=2 GHz
BW=1 GHz
BW=0.5 GHz
BW=2 GHz
Source: B. Petrachenko: Broadband Delay Tutorial, FRFF Wettzell 2009
7The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
VLBI 2010 requirements
VLBI 2010
What are the requirements for a new observation
system to fulfill the VLBI 2010 specifications?
� A fast moving antenna system with an antenna diameter of 12m or higher
� A broadband receiving system at least from 2 to 14 GHz, with an optional receiver at Ka-Band
� S- und X-Band compatibility (RCP)
� stable phase centre and stable reference point
� high antenna efficiency and low system temperature
� Improved reference and calibration systems
� New digital data acquisition systems
8The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
TWIN - Radioteleskop
Technical Data:
� Main reflector: 13.2m
� Ringfocal-Design
� f/D = 0.29
� Path Length Error <0.3mm
� ALMA Mounting with drive velocities of 12°/s in Azimuth and 6°/s in Elevation
� Balanced antenna design
� Excellent bearings
� 27Bit Encoder : 0.0003°resolution
� Subreflector adjustable by a Hexapod
9The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
TWIN – Radioteleskop: Path Length Error
Definition: Path Length Error
�Lnot_deformed = L1+L2+L3+L4
�Ldeformed = (L1+dL1)+(L2+dL2)+
(L3+dL3)+(L4+dL4)
�L_Error = Ldeformed - Lnot_deformed
elevation axis
L1
L2
L3
L4
P1=P1'
P2
P3
P4
P5
not deformed
deformed
focus ellipse
focus feed
main reflector
subreflector (ellipse)
feed cone
P3'
P4'
P2'
P5'
L1 = distance main axis – reflector surfaceL2 = distance reflector surface – subreflectorL3 = distance subreflektor – feed focus
L4 = distance feed focus – axis intersection point
The TTW-Antenna is designed for a Path Length Error of less than 0.3mm !!
( )
∑
∑
=
=
⋅
=192
1
192
1
i
i
i
ii
A
ErrorPathLengthA
ErrorPathLength
Source: Vertex Design Review; Dez. 2008
10The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
TWIN Radioteleskop: Hauptreflektor
13.2m Ring Focus Antenna
Aperture Field Distribution, f = 5 GHz
-25
-22.5
-20
-17.5
-15
-12.5
-10
-7.5
-5
-2.5
0
-6.5 -6 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5
rho [m]
Rela
tive
Am
pli
tud
e [
dB
]
13.2m Antennas with Gaussian Beam Feeds (-12dB at Subreflector Rim)
Aperture Effenciency
60
65
70
75
80
85
0 2 4 6 8 10 12 14 16 18
Frequency [GHz]
Ap
ert
ure
-Eff
icie
nc
y [
%]
Gregory-Antenna
Dualoffset-Antenna
Ringfocus-Antenna
Distribution of the radiated energy Effective beam efficiency
Ringfocal-Design• Dual-Reflector receiving system
• optimal for large flare angles
• no blockage by the subreflector
• high illumination efficiency
• the feed horn is prevented by
radiation from the sun
Source: Willi Göldi, Mirad; FRFF-Workshop 2009, Wettzell
11The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Broadband Receiving System: Triband-Feed
3 d B / 9 0 °
T u r n s t i l e
H o r n S - B a n d
H o r n X - B a n d
X / R H C P
X / L H C P
3 d B / 9 0 °
K a / L H C P
K a / R H C P
S / L H C P
S / R H C P
P o l a r i z e r
S e p t u m
H y b r i d
H y b r i d
S - B a n d
X - B a n dT u r n s t i l e
F e e d K a - B a n d
B P F
B P F
B P F
B P F
B P F
B P F
X / R H C P
X / L H C P
K a / L H C P
K a / R H C P
S / L H C P
S / R H C P
L N A
L N A
L N A
L N A
L N A
L N A
D e w a r
Dewar for the Triband-Feed
Schematic Triband-Feed
12The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Broadband-Receiving-System: Eleven-Feed
Design proposal for the Eleven-Feed
Quelle: A. Emrich; Omnisys.; Schweden
Principle Schematic
Design Proposal Dewar
13The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Receiving-System: Wideband-Receiver
Phase-Calibrationsystem
MW-Filter
0 -14 GHz
NoiseCal
Injection
MW-Filter
MW-Filter
MW-Filter
0 -14 GHz
MW-Filter
20- 22GHz
MW-Filter
20- 22GHz
MW-Mixer
AmpAmp
Amp AmpAmp
Amp
MW-Mixer
MW-Mixer
MW-Mixer
RMS-Detector
Synthesizer
23 – 33 GHz
PLDRO
22.5 GHz
Phasetrack -Cable
MW-Kabel
MW-Kabel
H-Maser
LNA‘s
DAQ-SystemDBBC, DBE
MK5B, MK5C
FS-PC
5/1
0 M
Hz-
Dis
trib
uto
rZu den anderen Kanälen
VPol
HPol MK5
A/D
Controller
Feed/Dewar
Subreflectorhorn
14The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
February 2011
15The TWIN-Radiotelescopes Wettzell; 17th ILRS-Meeting 2011 - 16 -20th May 2011 Bad Kötzting
Mounting of the Telescopes