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BepiColombo: Ka-band Translator R. Giordani, L. Simone February 27, 2007

BepiColombo: Ka-band Translator R. Giordani, L. Simone February 27, 2007. 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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BepiColombo: Ka-band Translator R. Giordani, L. Simone February 27, 2007

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  1. BepiColombo: Ka-band Translator • R. Giordani, L. Simone • February 27, 2007

  2. 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

  3. 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

  4. X X X X CASSINI KaT Block Diagram • Fully analogue architecture 21 Fo Fo 315 Fo LNA 108 MHz IF 2 GHz IF 20 Fo 294 Fo HPLL (X5) Fo MULTIPL (X3) Fo MULTIPL (X2) LOOP FILTER LOCK DETECTOR SPLL (X49) 2 Fo MULTIPL (X2) LOCK STATUS 90° 0° VCXO SPE Fo BUFFER

  5. CASSINI KaT Allan Deviation • Allan Deviation requirement fully met  SPECIFICATION MEASURED VALUE Integration time: sec

  6. CASSINI KaT

  7. 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.

  8. MORE KaT Requirements EID-B KaT Requirements

  9. 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)

  10. KaT Digital approach example

  11. BepiColombo Radio-Frequency Subsystem • Preliminary configuration based on singleKa-Band amplifier (i.e. TWTA) serving both the DST and KaT down-links.

  12. 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): 1.510-4 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. On-Board Radio-Frequency Subsystem (DST + KaT) X-Band Antenna Ka-Band Antenna • 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 X-Band Antenna Ka-Band Antenna On-Ground Segment

  13. Scientific Requirements for Radio-Science Experiment (2/2) • Preliminary budget for Range Measurement (only on-board, including aging): KaT • 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 610-15 for the X/X section • y 110-14 for the X/Ka section

  14. 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.

  15. Architectural Issues (2/3) • Carrier recovery scheme • Phase detector and digital loop filter implemented in the digital domain (no quartz filter is needed). • EM DST uses 40 bit DDS. Relevant simulation results show good Allan deviation performance that will be verified by test within April.

  16. 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.

  17. TGA4209 TGA4514 TGA4514 Architectural Issues (3/3) • 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 + 5 dBm + 35.5 dBm + 20 dBm

  18. Intermodulation Effects on Ka-Band Down-Link (1/3) F1 @ 44 dBm 18 dB 2F1-F2 @ 26 dBm F2 @ 34 dBm 33.1 dB 18.9 dB 2F2-F1 @ 15.1 dBm 3F1-2F2 @ 10.9 dBm -1.5 dBm (max output power for in-band interference) • F1 = DST Frequency (31.9925 GHz) • F2 = KaT Frequency (32.180 GHz)

  19. Intermodulation Effects on Ka-Band Down-Link (2/3) DST KaT Compare with previous slide to identify the spurious signals order

  20. Intermodulation Effects on Ka-Band Down-Link (3/3) DST KaT (modulated)

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