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Design of a Combined Beacon Receiver and Digital Radiometer for 40 GHzPropagation Measurements at the Madrid Deep Space Communications Complex
www.nasa.govNational Aeronautics and Space Administration
Michael Zemba,1 James Nessel,1 David Morabito2 Presented by Michael Zemba1NASA Glenn Research Center, Cleveland, OH Advanced High Frequency Branch2Jet Propulsion Laboratory, Pasadena, CA
Session: Propagation I
23rd Ka and Broadband Communications Conference • Trieste, Italy • October 19th, 2017
https://ntrs.nasa.gov/search.jsp?R=20180000921 2020-07-11T18:02:55+00:00Z
Presentation Overview
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1. Motivation & Experiment Goals2. Site of Study3. Instrumentation & System Design4. Temperature Control5. System Performance6. Radiometer Calibration8. Concluding RemarksWireframe schematic of the Alphasat satellite carrying the Aldo Paraboni TDP#5 Experiment.
Motivation & GoalsExperiment Goals
• To assess the impact of atmospheric effects on links operating in the Q-band (rainattenuation, scintillation, etc.) in various climatological regions through distributedmeasurement campaigns.• To assist the development of physical models to improve predictions of atmosphericattenuation within the Q-band.NASA Motivation
• Preliminary architecture studies of the next generation TDRSS system will require higherdownlink bandwidths than available in the current Ku-band allocation• The allocation of 4 GHz of contiguous bandwidth in the Q-band provides an opportunity tomeet these requirements• NASA mission planning benefits greatly from Q-band measurements near NASA frequencyallocations at Deep Space Network sites.
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Launch of Alphasat on an Ariane 5, July 2013.(Photo: ESA / CNES / ARIANESPACE)
39.4 GHzAlphasat Q
19.7 GHzAlphasat Ka
Site of Study
4Beacon Receiver / Radiometer at the Madrid Deep Space Communications Complex
NASA Alphasat Stations (* The Madrid Deep Space Communications Complex is in Robledo de Chavela)
NAlphasat 40 GHz Beacon Receiver
NASA Madrid Deep Space Communications Complex
R o b l e d o d e C h a v e l a,S p a i n
MDSCC, Spain
GroundStation
Installation Date March 2017
Latitude 40.425433° N
Longitude 4.251175° W
Altitude 758 m
Satellite
Name Alphasat
Nom. Elevation 34.5°
Nom. Azimuth 139°
Beacon Freq. 39.402 GHz
Edinburgh
Milan
Madrid*
Instrumentation
Antenna Gain 45.6 dBiAntenna Beamwidth 0.9 deg
Antenna Tracking Resolution 0.01 degLNA Gain 33 dB
LNA Noise Figure 2.5 dBBeacon Frequency 39.402 GHz 5
Final IF 5 MHzMeasurement Rate 10 Hz and 1 Hz
Dynamic Range 30 dBTemperature Control 0.01 deg C (plate) / 1 deg C (air)
Radiometer Calibration 20 sec / 30 minRadiometer Bandwidth 10 MHz
GRC Beacon Receiver JPL Interferometer Element RF Electronics IF Electronics
System Block DiagramThe beacon is downconverted from 39.402GHz to 70 MHz in two stages at the feed,then transmitted over fiber to the finaldownconversion (to 5 MHz) anddigitization.A waveguide switch prior to the LNA is usedfor radiometer calibration via Noise Diode,and calibration is also done via automatedtipping once per day.All LOs are referenced to a common ultra-stable 10 MHz ref. oscillator.Temperatures are all tightly controlled:• TLNA temperature controlled within ±0.1°C• TRFplate temperature controlled within ±0.01°C• TND temperature controlled within ±0.5°C
Fine-Tuning Polarization Alignment↷ Clockwise, as Viewed from Rear (+)↶ Anticlockwise, as Viewed from Rear (-)
B A C K
0⁰
-80⁰ -10⁰
Alignment to the beacon polarization (Linear -45°) plus LNB skew at each site isaccomplished through mechanical rotation of the antenna on a custom mount. Onthe antenna mount, four mounting bolt holes swept from -10⁰ to -80⁰ allow fineadjustment of the polarization to cover all NASA Alphasat sites.
Edinburgh-62.7⁰
Milan-59.8⁰
Madrid-74.8⁰
Polarization,No Skew-45.0⁰
Site Pol. Skew Final
Milan, Italy -45.0⁰ ↶ -29.8⁰ ↶ -74.8⁰ ↶Edinburgh, Scotland -45.0⁰ ↶ -17.7⁰ ↶ -62.7⁰ ↶
Madrid, Spain -45.0⁰ ↶ -14.8⁰ ↶ -59.8⁰ ↶
-110⁰ ↶ -74.8⁰ ↶
Temperature Control System
Heatsink
RF Electronics
LNA
Antenna Feed /Noise Diode
Internal Air Temperature
Cold Plate
Heatsink
±0.01 °C
±0.1 °C
±2.0 °C
System temperature is tightly controlled to limit gain variation.
A primary thermoelectric cooling (TEC) system controls a cold-plate withinthe RF enclosure to within ±0.01 °C. All mountable RF components areheatsinked to this plate including LOs, IF amplifiers, and filters. The noisediode is also heatsinked to this plate.
The LNA is mounted directly to the waveguide switch / feed and cannot beheatsinked to the cold plate. Instead, a secondary TEC system controls theLNA to within ±0.1 °C.
The internal air temperature of the enclosure is circulated with a fan andmaintains stability within about ±2.0 °C day-to-day with some largerseasonal drift.
C2-25
C2-40 C2-40
C2-40 C2-40
- PWM +
PWM +-
The TEC systems use four Tellurex C2-40 tiles (plate) and one C2-25 (LNA) driven by a PWM voltage.
The plate tiles are driven as two parallel pairs of two series tiles.
Temperature Stability04/19 04/20 04/21 04/22 04/23
39.95
39.96
39.97
39.98
39.99
40
40.01
40.02
40.03
40.04
Plat
e Te
mp
(°C)
Time (UTC)04/19 04/20 04/21 04/22 04/23
43.5
43.6
43.7
43.8
43.9
44
44.1
44.2
44.3
44.4
44.5
LNA
Tem
p (°C
)
Time (UTC)
04/19 04/20 04/21 04/22 04/2334.5
35
35.5
36
36.5
37
37.5
38
38.5
39
RF A
ir Te
mp
(°C)
Time (UTC)04/19 04/20 04/21 04/22 04/2337
37.5
38
38.5
39
39.5
40
ND T
emp
(°C)
Time (UTC)
±0.01 °C ±0.1 °C
±2.0 °C
±0.5 °C
RF Plate Temperature LNA Temperature
RF Air Temperature Noise Diode Temperature
4 Day Temperature Stability
03:45 04:00 04:15 04:30 04:45 05:00 05:15 05:30 05:45 06:00152
153
154
155
156
157
158
159
Beac
on F
requ
ency
(kHz
)
Time (UTC)
03:45 04:00 04:15 04:30 04:45 05:00 05:15 05:30 05:45 06:00-75
-70
-65
-60
-55
-50
-45
-40
CH1
Pow
er (d
Bm)
Time (UTC)
10
Under normal operating conditions, thebeacon receiver tracks the signal using amodified Quinn-Fernandes frequencyestimation algorithm.When attenuation approaches the noisefloor (below a given power threshold), thefrequency estimate is replaced by anaverage of the frequency estimate prior tothe fade. This allows for a slightimprovement in dynamic range during thebeginning and end of deep fades.Signal lock is immediately regained whenthe signal reappears above the noise floor.
System PerformanceTracking Threshold
Beacon tracked from frequency estimate prior to rain fade.
Loss of Lock
30 dB Dynamic Range
4.5 dB Antenna Wetting
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The digital radiometer measurement is implemented bypre-processing the sampled data before calculating thesignal power.The full bandwidth output from the final-stage filter isNyquist sampled to obtain the noise power measurement.A digital notch filter is applied, centered on a movingaverage of past beacon frequency estimates, to remove thesignal power. The remaining noise power is then integratedto produce the noise power measurement.The signal power is obtained by applying a digital band-pass sampling around the beacon frequency, thendecimating to reduce the computational demand of the FFT/ frequency estimators used to estimate signal power.
Digital Radiometer DesignNyquist Sampled Spectrum
(fs/2 = 5.55 MHz)
Noise Power SpectrumNotch Filter @ Beacon Frequency →
Integrate Noise Power
Signal SpectrumBPF @ Beacon Frequency →Decimate / Undersample →
Estimate Frequency (QNF) → Calculate Signal Power
fs 11.11 MHzN 220 (1,048,576)
Decimation 25 (32)BPF Bandwidth 50 kHz
Notch Bandwidth 2 kHzFilter Type Chebyshev II
Filter Order 10Filter Atten. 100 dB
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Digital Radiometer Measurement09 10 11 12
-58
-56
-54
-52
-50
-48
-46
-44
-42
CH1
Pow
er (d
Bm)
Time (UTC)
09 10 11 12-32.5
-32.45
-32.4
-32.35
-32.3
-32.25
-32.2
-32.15
-32.1
-32.05
-32
Mea
n No
ise
Pow
er (d
Bm)
Time (UTC)
Integrated Noise Power
Signal Power
16 dB Rain Fade
0.5 dBm Noise Power Variation
22:10 22:15 22:20 22:25 22:30 22:35 22:40 22:45 22:50-32.9
-32.85
-32.8
-32.75
-32.7
-32.65
-32.6
-32.55
-32.5
-32.45
-32.4
Mea
n No
ise
Pow
er (d
Bm
)
Time (UTC)
01:17 01:18 01:19 01:20 01:21 01:22-33
-32.5
-32
-31.5
-31
-30.5
-30
Mea
n No
ise
Pow
er (d
Bm)
Time (UTC)
Digital Radiometer Calibration
90°
Tip Calibration
Noise Diode Calibration
45° 30°20°
15°
10°
Nominal (35 °) Nominal (35 °)
Antenna
Noise Diode
Antenna
OnOff
Tip Calibration
MDSCC Receiver during tip calibration at 90° elevation angle.
Concluding Remarks & Future WorkConclusions
• The MDSCC Alphasat terminal has been operational since March 2017, collecting attenuation and scintillation data at an elevationangle of 34.5°. Operation is expected to continue for a minimum of 5 years.• The integrated digital radiometer provides valuable clear sky reference level but requires calibration – this system used a switching noise diode approach as well as a tip calibration and found that tip calibrations are sufficient and may be preferable to minimize required hardware.Future Work
• Infusion of data into MDSCC high-frequency operations.• Antenna wetting resolution – feed cover with hydrophobic coating
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Thank You!Thank You!
Thank You!
Appendix Charts
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Contact InformationJames NesselPrincipal Investigator, RF Propagation [email protected] ZembaResearch [email protected] SchemmelResearch [email protected]
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NASA Glenn Research Center21000 Brookpark Rd. MS 54-1Cleveland, Ohio 44135, USA