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January 2007
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BepiColombo: Ka-band Translator
R. Giordani, L. Simone
February 27, 2007
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Outline
AAS-I Heritage: Cassini KaT Equipment Main Performance Architecture & Frequency Plan Allan Deviation Test Result Anomaly during Mission
Goals of MORE/KaT Phase A/B1
Architectural Issues & Trade-Offs
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CASSINI KaT Performance
• Coherent frequency Translator which converts the received signal (34 GHz) with a ratio of 294/315 (32 GHz) for Doppler testing purposes.
• Satisfy stringent requirements in terms of phase noise and Allan deviation.
• C/No > 32 dBHz
• Acquisition Probability > 99%
• Acquisition Time: less than 10 min
• Doppler Range: 350 KHz• Doppler Rate 320 Hz/sec
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108 MHz IF2 GHz IF
CASSINI KaT Block Diagram
Fully analogue architecture
LNA
MULTIPL
(X3)
XX
SPLL
(X49)
HPLL
(X5)
MULTIPL
(X2)
MULTIPL
(X2)
BUFFERVCXO
LOCK DETECTOR
LOOP FILTER
XX
315 Fo
294 Fo
21 Fo Fo
20 Fo
2 Fo
FoSPE
90° 0°LOCK STATUS
FoFo
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CASSINI KaT Allan Deviation
SPECIFICATION
MEASURED
VALUE
Integration time: sec
Allan Deviation requirement fully met
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CASSINI KaT
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January 2007
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CASSINI KaT Anomaly
• During the cruise (in Jupiter gravitational field), an anomaly occurred at KaT level: the Unit rest frequency shifted about 13 MHz from the nominal value.
• The explanation is based on the assumption that the varactor (hyperabruct type) used in the 109 MHz VCXO modified its voltage/capacitance characteristic by the effect of low dose radiations/static charges.
• The varactor operates by the charges stored at the reverse biased junction. A modification of this environment may change the intrinsic capacitance characteristic.
• The effects of the varactor degradation have been proven on a VCXO breadboard, experiencing the same behavior of the flying circuit.
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MORE KaT Requirements
EID-B KaT Requirements
Uplink frequencies 34.31 GHz (TBC) Downlink frequencies 32.02 GHz (TBC) Translation ratio (Fr/Ft) 15/14 Uplink RF level -105 dBm (nominal) Noise figure <5 dB (nominal) RF output level 1 dBm (nominal) Up-link Tracking Range 1 MHz Allan Deviation 1510 (=1000 sec) WBRS Ranging Channel
Tone frequency
Delay accuracy (calibrated)
20 MHz
<0.5 nsec
Output spurious - 50 dBc DC power consumption: 16 W Mass 3.25 Kg (max)
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MORE/KaT: Phase A/B1 Overview
MORE/KaT Phase A/B1 Schedule: Start Event (To): Kick-Off (15/01/2007) End Event (To + 16): KaT detailed specification (15/05/2008)
MORE/KaT Phase A/B1 Main Goals: Scientific Requirements Analyses KaT Architectural Design KaT Requirement Specification KaT B/B of Critical Components (Allan Variance Test)
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KaT Digital approach example
Digital Module
TCXO
Ftx=2940F1+KFd
2932
F1
Frx=3150F1+Fd
Receiver Analogue Module
DAC207F
1
32F
1
Ka-Band Transmitter Module
F1+KFd
SAW
x4
2700
F1
PhaseMod.
4F1
FPGA
Ftx=315FFtx=294FF1=F/10
S-Band Section (218F1)
207F
1
1st IF Section (11F1)
675F
1
x4
Frequency Generationbased on Integer-N PLL
733F14F1
240F1+KFd
MLC
DS16
WBRS Channel
A
Frequency Generation & WBRS Module
A
2nd IF Section (5F1)
DACx2
218F1+Fd 11F1+Fd
6F1+
Fd
5F1
3F1+Fd/2
ADC
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BepiColombo Radio-Frequency Subsystem
Preliminary configuration based on single Ka-Band amplifier (i.e. TWTA) serving both the DST and KaT down-links.
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January 2007
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Scientific Requirements for Radio-Science Experiment (1/2)
The main requirements concerning the BepiColombo radio-science experiment are summarized hereafter:
range accuracy: 15 cm (on-board contribution only) range-rate accuracy (integration time 1000 – 10000 s): 1.510-4 cm/s (overall
link) Multi-frequency link equations have to be taken into account when
apportioning the top-level requirement over X/X, X/Ka and Ka/Ka links.
XKXXKK 35
1
13
1
On-BoardRadio-Frequency Subsystem
(DST + KaT)
On-Ground Segment
KK rms of the observable relevant to Ka/Ka link XX rms of the observable relevant to X/X link XK rms of the observable relevant to X/Ka link
Ka-Band Antenna
Ka-Band Antenna
X-Band Antenna
X-Band Antenna
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Scientific Requirements for Radio-Science Experiment (2/2)
Preliminary budget for Range Measurement (only on-board, including aging):
Group Delay Variation (ns-pk-pk)Ka/Ka 1X/X 2.5X/Ka 2.5Overall 1.26
Range Error (cm-rms)9.5
Range Measurement
Preliminary budget for Range-Rate Measurement (overall):
In order to meet the required range rate accuracy, the following preliminary requirement can be considered for 1000 s of integration time: y 10-15 for the Ka/Ka section y 610-15 for the X/X section y 110-14 for the X/Ka section
KaT
Allan DeviationKa/Ka 8.00E-15X/X 5.00E-14X/Ka 1.00E-13Overall 1.5E-14
Range Rate Error (cm/s-rms)2.2E-04
Range Rate Measurement
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Architectural Issues (1/3)
Selection of the Ka/Ka turn-around ratio (up-link over down-link frequency ratio): Cassini figure: 315/294 ECSS current figures: 3599/3344, 3599/3360, 3599/3328 NASA proposal in the frame of CCSDS SLS-RFM meeting (07-03-2007):
3611/3360– “Proposed Additional Ka/Ka Transponder Turnaround Ratios for the 31.8-
32.3 GHz and 34.2-34.7 GHz Band, Category-B”, S. Kayalar, C. C.Wang, JPL
Selection of the equipment frequency plan: Inclusion of digital capabilities allows to easily demodulate the up-link
ranging channel.
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January 2007
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Architectural Issues (2/3)
Carrier recovery scheme Phase detector and digital loop filter implemented in the digital domain
(no quartz filter is needed).
10-1
100
101
102
10-18
10-17
10-16
10-15
10-14
10-13
10-12
10-11
10-10
Integration Time (sec)
Alla
n D
evia
tion
(rm
s)
Effect of Phase & Frequency Quantization on the Down-Link Allan Deviation
Simulation Results
ESA Mask EM DST uses 40 bit DDS. Relevant simulation results show good Allan deviation performance that will be verified by test within April.
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January 2007
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Architectural Issues (3/3)
Selection of Ranging scheme and relevant clock frequency (4 ÷ 8 MHz) Best candidate is the PN Ranging with flexible majority voting
(Tausworthe approach) already implemented on the X/X/Ka DST.
On-board calibration based on phase measurement (digital PLL approach) This capabilities appears fundamental to ensure the required group
delay stability (1 ns-pk-pk) and to overcome potential drift due to the aging.
This approach is also pursued in the X/X/Ka DST equipment for testing purpose.
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January 2007
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Architectural Issues (3/3)
TGA4209
TGA4514
TGA4514
+ 20 dBm
+ 5 dBm+ 35.5 dBm
Use of dedicated SSPA to avoid intermodulation effects in Ka-Band (see next slides) due to the simultaneous amplification of both the DST and KaT down-link carriers. The RF output power level (2.5 W) can be obtained putting in parallel two
power MMICs from TRIQUINT This configuration has η = 20% excluding DC/DC converter efficiency
+ 20 dBm
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January 2007
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Intermodulation Effects on Ka-Band Down-Link (1/3)
•F1 = DST Frequency (31.9925 GHz)•F2 = KaT Frequency (32.180 GHz)
F1 @ 44 dBm
F2 @ 34 dBm
2F2-F1 @ 15.1 dBm
2F1-F2 @ 26 dBm
3F1-2F2 @ 10.9 dBm
18.9 dB
18 dB
33.1 dB
-1.5 dBm (max output power for in-band interference)
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January 2007
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Intermodulation Effects on Ka-Band Down-Link (2/3)
DST
KaT
Compare with previous slide to identify the spurious signals order
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January 2007
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Intermodulation Effects on Ka-Band Down-Link (3/3)
DST
KaT (modulated)
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