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STAR Light PDR – 3 October 2001

SYSTEM REQUIREMENTS Roger De Roo 734-647-8779, deroo@umich.edu. STAR Light PDR – 3 October 2001. Outline: Science requirements & instrument concept STAR and DSDR technologies, instrument configuration Platform requirements (power/weight/balance) Flowdown requirements

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STAR Light PDR – 3 October 2001

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  1. SYSTEM REQUIREMENTS Roger De Roo 734-647-8779, deroo@umich.edu STAR Light PDR – 3 October 2001

  2. Outline: • Science requirements & instrument concept • STAR and DSDR technologies, instrument configuration • Platform requirements (power/weight/balance) • Flowdown requirements • Noise Budget, sampling, interference rejection • Calibration Outline

  3. Science Requirements Soil Moisture Monitoring (L-band radiometer w/ 4K accuracy) Land Surface Process Model Development (long term operation, plot scale ) Polar Operations (airborne access only) STAR-Light Design Goals Measurement Objectives

  4. Platform Requirements STAR-Light Design Goals Aircraft Sensor Concept STAR-Light Control Module STAR-Light Sensor Module For weight stability, plane must be a tail-dragger rather than equipt with tricycle gear

  5. Science Requirements Soil Moisture Monitoring: Radio astronomy band: 1400 – 1427 MHz Noise Equivalent Brightness Uncertainty (NEDT) < 0.5 K Land Surface Process Model Development in Polar Regions: Swath out to +/- 35 deg from sensor normal Daily operations for 3 hours near dawn Synthetic beamwidth from 15 deg to 22 deg Ambient thermal environment –30C to +40C (243 K to 313 K) STAR-Light Design Goals Derivative Measurement Objectives

  6. Platform Requirements Max altitude: about 3000m (higher requires oxygen) Min altitude: about 300m (lower sacrifices safety) Surface to altitude temperature difference: -30C typical Surface to altitude pressure change: 1000mb to 700mb typical STAR-Light Design Goals Aerial Environment

  7. Cold Plate Analog Digital Antenna Radome Sensor Concept: Configuration Mechanical arrangement on aircraft belly Cold Plate Receiver Cross section Receiverassembly is a field-replaceable unit

  8. Sensor Concept STAR-Light Aircraft Sensor Concept Use Synthetic Thinned Array Radiometry to -provide imaging capability -achieve multiple angle of incidence electronically -keep the sensor robust to partial failures Use Direct Sampling Digital Radiometry to -move complexity of STAR from analog to digital domain -keep the sensor head compact -reduce component count requiring thermal control

  9. o 90 Vi Vq Sensor Concept: STAR STAR-Light Concept: STAR Technology Different antenna baselines sample different spatial Fourier components of the scene f Baseline d Vi + j Vq = Tb(f) F1(f) F2(f) exp(j 2 p sin f d / l ) df *

  10. A/D DSP Vi Vq A/D Sensor Concept: DSDR Direct Sampling Digital Receiver Technology • Transfer • Noise bandwidth definition • I/Q detection (Hilbert transform) • Complex correlation • from analog to digital domain

  11. 2l/2 l/2 3l/2 l/2 Sensor Concept STAR concept Use a standard antenna array with missing elements: 7l/2 To simulate an array of larger dimensions, by using each Element in turn as the phase center of the array: + = 14l/2

  12. Sensor Concept STAR-Light Antenna Configuration: 1-D vs 2-D STAR 1-D: requires long antenna elements to achieve narrow beam -single angle of incidence (pushbroom operation) -alias free spacing is 0.500 l -demonstrated (ESTAR) 2-D: requires electrically small antenna elements -multiple angles of incidence (snapshot imaging) -many configurations; 3-arm appears optimal -alias free spacing is 0.577 l -proposed (SMOS), but not yet demonstrated

  13. Sensor Concept STAR Issues Huge sidelobes: STAR requires an aperture taper which increases synthesized beamwidth by a factor of 2 (canceling the aperture doubling) ………but the advantages of thinning remain Optimal taper is Blackmann [Camps etal ’98] Increased noise: Noise in STAR image = Real Aperture Area . Noise in real aperture pixel Actual Aperture in STAR ………but longer dwell time for STAR to reduce noise equals time required to scan the real array or real aperture [LeVine ’90, Ruf ’88]

  14. STAR-Light Antenna Design: Inter-element spacing Brightness Scene STAR image A trade-off between *reduction of field of view due to aliasing (ie. Grating lobes) against *loss of beam sharpness due to reduced array size Ideal spacing is about d=0.75 l to achieve 35deg FOV d=0.800 l d=0.577 l Flowdown Rqmt: Antenna Spacing

  15. Sensor Concept STAR Image Generation: Gain Correction {V(GT)}=F(GT) T=F-1(V(GT))/G T=F-1(V(GT))/F-1(V(G)) G is gain pattern of commercial patch antenna; Correction is not as pronounced for G=cosnq FOV=35o

  16. Flowdown Rqmt: Antenna Elements Pattern knowledge requirement Errors induced by imperfect knowledge of antenna gain patterns: Image DC offset = +30mK/K/deg2 + 12mK/K/%2 Image rms error = +/- 0.4 mK/K/deg +/- 0.35 mK/K/% Constant brightness temperature scene inverted by system with gain pattern uncertainty of 1dB and 10o Goal is 0.5dB and 5o

  17. Sensor Concept STAR Image Generation: Impulse Response cos2q 0o 30o 60o 89o patch antenna Array spacing driven by horizon alias generation d=0.68l = 14.4 cm

  18. A/D DSP Low Precision and Control: 2.0C High Precision and Control: 0.011C keep in operating range High Accuracy Monitoring: 0.1C; Moderate Control Sensor Concept: Thermal Heat Dissipation and Thermal Control 150 mW steady; 2.9 W intermittent 54 W typical; 70 W maximum 27 W steady

  19. Sensor Concept: Geometry Mechanical arrangement Preferred Orientation for Cold Plate: easy side access for cooling fluid conduits Required Orientation for Linear Pol Antennas: Parallel or anti-parallel AD Analog side needs high precision control, moderate heat removal Digital side needs low precision control, large heat removal AD Problem: orientation of cold plate to antenna

  20. A D A D A D A D Sensor Concept: Receiver Module Solutions to Cold Plate / Antenna Orientation Conflict Solution 0: disconnect Antenna from Receiver to allow Receiver orientation to Cold Plate Very difficult field cal Solution 2: multiple fixed Antenna & Receiver modules Expensive Cold Plate A D Antenna Solution 1: flexible connection between Antenna & Receiver to allow Receiver orientation to Cold Plate Questionable quality Solution 3: Circular Polarized Antennas Tricky Cold Plate A D Antenna

  21. Flowdown Rqmt: Antenna Elements Single Feed Circular Polarization Patch Notches create two modes w/ different resonances Proper feed allows these two modes to be fed w/ equal amplitude and 90o phase 1.4% circular polarization bandwidth at AR=1dB while 11% VSWR bandwidth (VSWR=2) Q=8.6; Eff=90% Cupped design to reduce mutual coupling Parameters shown from design paper; must be modeled w/ EM analysis SW 14cm 7.75cm e=2.2, t=4.6mm

  22. Platform Capabilities STAR-Light Design Goals Aircraft Capabilities Aircraft acquisition costs and aircraft integration are not part of STAR-Light project

  23. Platform Requirements: Weight Aviat Husky Weight Limitations Max. Gross Weight: 2000 lbs (normal category)

  24. Platform Requirements: Weight Useful Load Weight Breakdown * Present estimate + 10 lbs Weight Margin: 4 lbs (from previous viewgraph)

  25. Platform Requirements: Balance Weight and Balance w/ full fuel tanks w/ empty fuel tanks

  26. Platform Requirements: Power Constant Power Requirements

  27. Platform Requirements Intermittent Power Requirements Aircraft systems Taxi/Landing Lights (14.2A @ 12V) = 170.4 W Radio Transmissions (6A @ 12 V) = 72 W STAR-Light Components: RF switches: 2.9W at 0.3% duty cycle = 10mW Cooling System on climb to altitude

  28. 50 50 40 40 30 30 20 20 10 10 0 0 -10 -10 -20 -20 -30 -30 Sensor Concept: Thermal Increase in altitude to 3000 m Cooling Control Setpoints Ground Ambient Airborne Ambient

  29. Flowdown Requirements Integration Time for STAR-Light: 2x Husky no-flap stall speed

  30. Flowdown Requirements Integration Time for STAR-Light: Slower speed

  31. Flowdown Rqmt: Noise Figure For any taper [Camps, ’98]: DT dW=constant NEDT(uniform) = dW(Blackman)/dW(uniform) * NEDT(Blackman) = (15deg)^2 / (10deg)^2 * 0.5 K = 1.12K For uniform taper [LeVine, ’90], NEDT = TsysAsyn = Trec + 300K 73 sqrt( B t ) n Ael sqrt( 20e6 . 1.5 ) 10 For NEDT < 1 K, Tsys< 750 K or Trec<450 K (NF < 4.1 dB)

  32. Flowdown Rqmt: Noise Figure Antenna Low Noise Amp Miteq Cal injection Teledyne switch Interference Reject Filter IMC IL=0.60dB NF=0.80dB IL=0.45dB IL=0.25dB Interconnect losses < 0.5dB Downstream components: add 0.1dB System Noise Figure = 2.7 dB (Trec=250K)

  33. Flowdown Rqmt: Gain Signal amplitude at ADC must be > 4 levels (2 bits) for bias levels to not matter [Fischman, ’01] At Tsys=250K, k Tsys B = -101.6 dBm; LSB=15.63mV for typical ADC (SPT7610) => Padc=-26.6 dBm Overall gain must be > 75 dB For amplifier w/ G=26dB, 3 amplification stages minimum (to allow for losses in receiver, use 4 stages)

  34. Flowdown Rqmt: Gain Fluctuations Temperature fluctuations => Gain fluctuations => system noise dG/dT = -0.02 dB/K per gain stage dG/dT = -0.08 dB/K for system: requires 2mK rms to keep gain fluctuation component < fundamental NEDT Thermopad: temperature compensating attenuator Thermopads come in loss coefficient increments of 0.01 dB/K Goal: Use Thermopads to get system to +/- 0.015 dB/K; thermal control to 11mK rms

  35. Flowdown Rqmt: ADC levels Need a minimum of 4 levels for darkest target [Fischman ’01] Is a 3-bit Analog to Digital Converter (ADC) enough? Tsys(max) / Tsys(min) < (8 levels)^2 / (4 levels)^2 = 4 where Tsys=Tb+Trec If we wish to look at the sky, Tb(min)=~0K; On Earth, Tb(max)=~300K Then, Trec>100K or we need more bits Therefore, 3 bit ADC is enough

  36. Flowdown Rqmt: Pre-Sampling Filter IMC Ceramic Filter The Fringe Wash Function measures the differences between bandpass filters, and reduction in measurable visibility due to receiver differences • A pre-sampling filter is used to • define sampled bandwidth: • interference rejection • out-of-band noise rejection FWF=0.996

  37. Flowdown Rqmt: Pre-Sampling Filter IMC Ceramic Filter The half-bit level for a 3-bit ADC is –24dB Variations over temperature define the bandwidth extent for sampling

  38. Flowdown Rqmt: ADC sampling Sampling Rate considerations [Feixure etal ’98] For a noise bandwidth (approx -3dB BW) of 1403 – 1423 MHz, the sampled bandwidth (approx –24dB BW) is 1390 – 1435 MHz For I/Q demodulation, 2fH/m < fs < 2fL/(m-1), where m=1,2,…mmax and mmax=floor[fH/(fH-fL)] 92.58 MHz < fs < 92.66 MHz or 95.67 MHz < fs < 95.86 MHz or 98.97 MHz < fs < 99.29 MHz or 102.5 MHz < fs < 102.96 MHz… fs=102.8 MHz

  39. Flowdown Rqmt: ADC sampling Sampling skew: If |tskew| < 6.7 ns, reduction in visibility envelope is less than 3% ENV=sinc(Btskew) Vi=ENV*cos(2pf0tskew) Vq=ENV*sin(2pf0tskew) Fischman was unable to verify this form for the envelope Verification is a primary objective of the two channel system

  40. Flowdown Rqmt: ADC sampling Sampling jittersd produces a Coherence Loss (CL) in a visibility value [Fischman ’01]: CL = 10 log( 1 + ( 2 p f0sd)^2) for sd = 20 ps, CL = 0.14 dB, or, in other words, 20 ps jitter reduces a visibility value by 3% over a zero jitter visibility

  41. Flowdown Rqmt: Noise Budget x (73/10)x(0.45)= x 3.25

  42. Flowdown Rqmt: Interference • Keep cultural sources of RFI out of receiver chain to the extent that • Amplifiers do not saturate • Intermodulation products do not get generated in Radio Astronomy band • RFI does not alias into ADC sampling window • Some worst-case sources of interference: • 1. Air Traffic Control Radar Beacon System (ATCRBS) Transponder • *Responds to 1030 MHz radar pings, reporting aircraft altitude to ATC • *Transmits from the STAR-Light aircraft at 1090 MHz w/ peak power • between 70 and 500 W (+48 dBm to +57 dBm) • Air Route Surveillance Radar (ARSR) • * Transmits from the ground from 1250 to 1350 MHz w/ peak power up • to 5 MW (+97 dBm) • * Some similar military systems have high resolution modes which use • up to 1375 MHz, 1380 MHz, or 1400 MHz

  43. 140 dB- 156 dB 31 dB 51 dB 76 dB 101dB Flowdown Rqmt: Interference Keeping the ATCRBS Transponder from saturating STAR-Light amplifiers +53 dBm Moving the transponder antenna to the top of the tail gives a distance of 4 m to STAR-Light Coupling < –42 dB at 4 m Typical model (Garmin GTX 320A) transmits 200W (+53dBm) at 1090 MHz 4 m Cumulative Rejection Needed: P1dB=+8dBm P1dB=+14dBm

  44. Flowdown Rqmt: Interference Keeping the ARSR 1250 - 1350 MHz intermodulation products out of the 1400 – 1427 MHz Radio Astronomy band Rqmt: Keep PIM < -140dBm At 50 km, ARSR-3 power at antenna terminals is Pr =–5dBm (assuming gain is down by 8dB, and polarization match = 50%) Miteq IIP3 = -9dBm Requires filtering of F= 37dB at 1350 MHz P2=Pr-F P1=Pr-2F PIM=2P2+P1-2IIP3 f (MHz) 1277+/-5 f1 1345+/-5 f2 1413+/-10 2f2-f1 We will get hit w/ intermodulation interference from ARSRs. ARSRs sweep at 5 rpm, and our recovery time is on the order of microseconds. (Subsequent stages also need protection from amplified f1 and f2; M/A Com amp has IIP3=-2dBm)

  45. Flowdown Rqmt: Interference Quadrant Engineering, Inc. Experience Scanning Low Frequency Microwave Radiometer (SLFMR) [Goodberlet ’00] • SLFMR system: • f = 1413 MHz; B = 100 MHz • Phased Array antenna, not STAR • Designed NEDT=0.3K; verified in lab • Observed NEDT=5K over water (Tb=100K) • in field tests 20 miles from interference source • (Norfolk, VA) STAR-Light Implication: With just 15dB of Interference Rejection Filtering, we can drive that interference NEDT down to 0.15K

  46. Calibration: Hardware List STAR-Light Calibration Design: Pre-flight / In-flight Calibration To calibrate each antenna-receiver channel, we need * a hot load * a cold load to estimate the receiver temperature and overall receiver gain To calibrate each pair of channels, we need * correlated noise * uncorrelated noise to estimate the receiver correlation in magnitude and phase

  47. Calibration: Warm + Cold Slope a Gain V(d=0) x2 Tb=300K Tb= 77K V(d=0) Tb -Trec 0K 77K 300K To calibrate each antenna-receiver channel, we need * a warm load * a cold load to estimate the receiver temperature and overall receiver gain

  48. Calibration: Warm + Hot Delay = t Vi DSP Tb=300K Vq Dt Delay = t + Dt To calibrate each pair of channels, we need * correlated noise * uncorrelated noise (to determine Vi, Vq offsets) to estimate the receiver correlation in magnitude and phase

  49. Calibration: Receiver Two-Point Cal STAR-Light Calibration Design: Two-Point Calibration of a single channel Trec=300K B=20MHz t=1.5 s

  50. Calibration: Cold Noise Source STAR-Light Calibration Design: Quality of Cold Load Phase Uncertainties: Reflection +/- 6 deg Transmission +/- 12 deg L=0.3 dB VSWR=1.1 L=0.4dB VSWR=1.1 RCVR VSWR=1.1 50W at 77K VSWR=1.05

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