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January 2007

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All rights reserved © 2007, Alcatel Alenia Space

BepiColombo: Ka-band Translator

R. Giordani, L. Simone

February 27, 2007

January 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

January 2007

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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

January 2007

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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

January 2007

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CASSINI KaT Allan Deviation

SPECIFICATION

MEASURED

VALUE

Integration time: sec

Allan Deviation requirement fully met

January 2007

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CASSINI KaT

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.

January 2007

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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)

January 2007

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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)

January 2007

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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

January 2007

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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.

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

January 2007

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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

January 2007

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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.

January 2007

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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.

January 2007

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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.

January 2007

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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

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)

January 2007

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DST

KaT

Compare with previous slide to identify the spurious signals order

January 2007

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DST

KaT (modulated)

january 2007 backnext all rights reserved © 2007, alcatel alenia space page 1 bepicolombo: ka-band...

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