the twin-radiotelescopes wettzell - nasa · the twin-radiotelescopes wettzell; 17th ilrs-meeting...

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;


Radioteleskop Wettzell

RTW: D=20m, S/X-Band; Velocities: 3°& 1.5°/s; Tsys=40K; 1Gbps;


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


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


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


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


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


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


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


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


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


Broadband-Receiving-System: Eleven-Feed

Design proposal for the Eleven-Feed

Quelle: A. Emrich; Omnisys.; Schweden

Principle Schematic

Design Proposal Dewar


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


February 2011


Mounting of the Telescopes

the twin-radiotelescopes wettzell - nasa · the twin-radiotelescopes wettzell; 17th ilrs-meeting...

Documents