STAR Light PDR – 3 October 2001

STARLight PDR 3 Oct ‘01 R De Roo System - Page D.1

STARLightSTARLightSTAR Light PDR – 3 October 2001

SYSTEM REQUIREMENTS

Roger De Roo

734-647-8779, [email protected]


STARLightSTARLight

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


STARLightSTARLightScience 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 GoalsMeasurement Objectives


STARLightSTARLightPlatform Requirements

STAR-Light Design GoalsAircraft Sensor Concept

For weight stability, plane must be a tail-dragger rather than equipt with tricycle gear

STAR-Light Sensor Module

STAR-Light Control Module


STARLightSTARLightScience Requirements

Soil Moisture Monitoring:Radio astronomy band: 1400 – 1427 MHzNoise Equivalent Brightness Uncertainty (NET) < 0.5 K

Land Surface Process Model Development in Polar Regions:Swath out to +/- 35 deg from sensor normalDaily operations for 3 hours near dawnSynthetic beamwidth from 15 deg to 22 degAmbient thermal environment –30C to +40C (243 K to 313 K)

STAR-Light Design GoalsDerivative Measurement Objectives



STAR-Light Design GoalsAerial Environment

Max altitude: about 3000m (higher requires oxygen)Min altitude: about 300m (lower sacrifices safety)Surface to altitude temperature difference: -30C typicalSurface to altitude pressure change: 1000mb to 700mb typical


STARLightSTARLightSensor Concept: Configuration

Mechanical arrangement on aircraft belly

Cross section

Cold Plate

Antenna

DigitalAnalog

Radome

Cold Plate

Receiver

Receiver assembly is a field-replaceable unit


STARLightSTARLightSensor 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


STARLightSTARLightSensor Concept: STAR

STAR-Light Concept: STAR Technology

Vi

90o

Vq

Different antenna baselines sample different spatial Fourier components of the scene

Baseline d

Vi + j Vq = Tb() F1() F2() exp(j 2 sin d / ) d*


STARLightSTARLightSensor Concept: DSDR

Direct Sampling Digital Receiver Technology

A/D DSP

A/D

Vi

Vq

Transfer • Noise bandwidth definition• I/Q detection (Hilbert transform)• Complex correlation from analog to digital domain



STAR concept

Use a standard antenna array with missing elements:

To simulate an array of larger dimensions, by using eachElement in turn as the phase center of the array:

+

=



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 -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 -proposed (SMOS), but not yet demonstrated



STAR IssuesHuge sidelobes: STAR requires an aperture taper which increases synthesized beamwidth by a factor of 2 (canceling the aperture doubling)………but the advantages of thinning remainOptimal 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]


STARLightSTARLightFlowdown Rqmt: Antenna Spacing

STAR-Light Antenna Design: Inter-element spacing

Brightness Scene

d=0.800

d=0.577

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 to achieve 35deg FOV

STAR image



STAR Image Generation: Gain Correction

{V(GT)}=F(GT) T=F-1(V(GT))/G T=F-1(V(GT))/F-1(V(G))

FOV=35o

G is gain pattern of commercial patch antenna;Correction is not as pronounced for G=cosn


STARLightSTARLightFlowdown 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



STAR Image Generation:Impulse Response

cos2

patch antenna

0o 30o 60o 89o

Array spacing driven by horizon alias generation d=0.68 = 14.4 cm


STARLightSTARLightSensor Concept: Thermal

A/D DSP

High AccuracyMonitoring: 0.1C;Moderate Control

High Precision and Control:0.011C

Low Precision and Control:2.0C

keep in operating range

Heat Dissipation and Thermal Control

27 W steady54 W typical;70 W maximum

150 mW steady;2.9 W intermittent


STARLightSTARLightSensor Concept: Geometry

Mechanical arrangement

Problem: orientation of cold plate to antenna

Preferred Orientation for Cold Plate: easy side access for cooling fluid conduits

Required Orientation for Linear Pol Antennas:Parallel or anti-parallel

A D

A D

Analog side needs high precision control, moderate heat removal

Digital side needs low precision control, large heat removal


STARLightSTARLightSensor Concept: Receiver Module

Solutions to Cold Plate / Antenna Orientation Conflict

Cold Plate

Antenna

DA

Solution 0: disconnect Antenna from Receiver to allow Receiver orientation to Cold Plate

Very difficult field cal

Cold Plate

Antenna

DA

Solution 1: flexible connection between Antenna & Receiver to allow Receiver orientation to Cold Plate

Questionable quality

Solution 2: multiple fixed Antenna & Receiver modules

Expensive

A D

Solution 3: Circular Polarized Antennas

Tricky

A D

A D

A D


STARLightSTARLightFlowdown 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

=2.2, t=4.6mm


STARLightSTARLightPlatform Capabilities

STAR-Light Design GoalsAircraft Capabilities

Parameter Aviat Husky A-1B Piper Super Cub PA-18 150

Power available 420 W ?

Carrying capacity

(pilot + instrument)

810 lbs 767 lbs

Min Safe Speed

(Stall Speed X2)

110 mph = 50 m/s 74 kts = 38 m/s

(40 deg flaps)

Availability New or used Used only

Aircraft acquisition costs and aircraft integration are not part of STAR-Light project


STARLightSTARLightPlatform Requirements: Weight

Aviat Husky Weight Limitations

Max. Gross Weight: 2000 lbs (normal category)

Design Empty Weight 1190 lbs

Equipment Changes 80 lbs

Std Zero Fuel Empty Weight

1270 lbs

Oil and Unusable Fuel 27 lbs

Equipped Weight Empty 1297 lbs

Fuel (50 Gal max) 300 lbs

Useful Load (excl. Fuel) 397 lbs

Gross Loaded Weight 1994 lbs


STARLightSTARLightPlatform Requirements: Weight

Useful Load Weight Breakdown

* Present estimate + 10 lbsWeight Margin: 4 lbs (from previous viewgraph)

Pilot* 200 lbs

Survival Package 20 lbs

Sensor Module* 83 lbs

Control Module* 70 lbs

Cabling 20 lbs

Pilot Interface 4 lbs

Useful Load (excl. Fuel) 397 lbs


STARLightSTARLightPlatform Requirements: Balance

Weight and Balance

CG Envelope

13001400150016001700180019002000

71 72 73 74 75 76 77 78 79 80

Inches Aft of Datum

Tak

e-o

ff G

ross

W

eig

ht

(lb

s) w/ full fuel tanks

w/ empty fuel tanks


STARLightSTARLightPlatform Requirements: Power

Constant Power RequirementsAvailable Power (70 A @ 12 V) 840 W

Essential Flight Loads (33.1A) 400 W

Power Available for STAR-Light 440 W

S-L Sensor Module (RF Amps) 27 W

S-L Sensor Module (Digital) 76 W

STAR-Light Control Module 15 W

STAR-Light Thermal Control 85 W

STAR-Light Direct Power Rqmt 203 W

STAR-Light Power Supply Losses 31 W

STAR-Light Total 232 W

Power Margin 208 W



Intermittent Power Requirements

Aircraft systemsTaxi/Landing Lights (14.2A @ 12V) = 170.4 WRadio Transmissions (6A @ 12 V) = 72 W

STAR-Light Components:RF switches: 2.9W at 0.3% duty cycle = 10mWCooling System on climb to altitude


STARLightSTARLightSensor Concept: Thermal

-30-20-10

0102030

5040

GroundAmbient

CoolingControlSetpoints

-30-20-10

0102030

5040

AirborneAmbient

Increase in altitude to 3000 m


STARLightSTARLightFlowdown Requirements

Integration Time for STAR-Light:2x Husky no-flap stall speed


STARLightSTARLightFlowdown Requirements

Integration Time for STAR-Light:Slower speed


STARLightSTARLightFlowdown Rqmt: Noise Figure

For any taper [Camps, ’98]: T d=constantNET(uniform) = d(Blackman)/d(uniform) * NET(Blackman) = (15deg)^2 / (10deg)^2 * 0.5 K = 1.12K

For uniform taper [LeVine, ’90],NET = Tsys Asyn = Trec + 300K 73 sqrt( B ) n Ael sqrt( 20e6 . 1.5 ) 10

For NET < 1 K, Tsys< 750 K or Trec<450 K (NF < 4.1 dB)


STARLightSTARLightFlowdown Rqmt: Noise Figure

Antenna

Cal injectionTeledyne switch

Interference Reject FilterIMC

Low Noise AmpMiteq

IL=0.45dB

IL=0.25dB

IL=0.60dB NF=0.80dB

Interconnect losses < 0.5dB

Downstream components: add 0.1dB

System Noise Figure = 2.7 dB (Trec=250K)


STARLightSTARLightFlowdown 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)


STARLightSTARLightFlowdown 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 NET

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


STARLightSTARLightFlowdown 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


STARLightSTARLightFlowdown Rqmt: Pre-Sampling Filter

IMC Ceramic Filter

A pre-sampling filter is used to define sampled bandwidth:• interference rejection• out-of-band noise rejection

The Fringe Wash Function measures the differences between bandpass filters, and reduction in measurable visibility due to receiver differences

FWF=0.996


STARLightSTARLightFlowdown Rqmt: Pre-Sampling Filter

The half-bit level for a 3-bit ADC is –24dB

Variations over temperature define the bandwidth extent for sampling

IMC Ceramic Filter


STARLightSTARLightFlowdown 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 or95.67 MHz < fs < 95.86 MHz or98.97 MHz < fs < 99.29 MHz or102.5 MHz < fs < 102.96 MHz… fs=102.8 MHz



Sampling skew:If |tskew| < 6.7 ns, reduction in visibility envelope is less than 3%

ENV=sinc(Btskew)Vi=ENV*cos(2f0tskew)Vq=ENV*sin(2f0tskew)

Fischman was unable to verify this form for the envelope

Verification is a primary objective of the two channel system



Sampling jitter produces a Coherence Loss (CL) in a visibility value [Fischman ’01]:

CL = 10 log( 1 + ( 2 f0 )^2 )

for = 20 ps, CL = 0.14 dB, or, in other words, 20 ps jitter reduces a visibility value by 3% over a zero jitter visibility


STARLightSTARLightFlowdown Rqmt: Noise Budget

Noise source Noise (K rms)

RCVR+Antenna

Noise (K rms)

Image (Blackman)

conditions

Fundamental .101 .326 Tsys=600 K

B=20MHz; =1.5s

Gain Fluctuations .080 .260 dG/dT = -0.015 dB/C

To = 11 mC rms

Passive Parts .004 .013 IL = 1.75 dB

To = 11 mC rms

Antenna .022 .072 Efficiency = 90% (IL=0.45dB)

To = 200 mC rms

Radome .022 .072 Efficiency = 95% (IL=0.22dB)

To = 400 mC rms

ADC .048 .156 dSpan/dT = 50 ppm/C

To = 200 mC rms

Total (RSS) .141 .460

x (73/10)x(0.45)= x 3.25


STARLightSTARLightFlowdown 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)

2. 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



Keeping the ATCRBS Transponder from saturating STAR-Light amplifiers

4 m

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

+53 dBm

Cumulative Rejection Needed:

31 dB 51 dB 76 dB 101dB140 dB-156 dB

P1dB=+8dBm P1dB=+14dBm



Keeping the ARSR 1250 - 1350 MHz intermodulation products out of the 1400 – 1427 MHz Radio Astronomy band

f (MHz)

1345+/-5f2

1277+/-5f1

1413+/-102f2-f1

P2=Pr-F

PIM=2P2+P1-2IIP3

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

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)

P1=Pr-2F



Quadrant Engineering, Inc. ExperienceScanning Low Frequency Microwave Radiometer (SLFMR) [Goodberlet ’00]

SLFMR system:

• f = 1413 MHz; B = 100 MHz

•Phased Array antenna, not STAR

•Designed NET=0.3K; verified in lab

•Observed NET=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 NET down to 0.15K


STARLightSTARLightCalibration: 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


STARLightSTARLightCalibration: Warm + Cold

To calibrate each antenna-receiver channel, we need* a warm load* a cold load

to estimate the receiver temperature and overall receiver gain

Tb=300K Tb= 77K

Tb

-Trec 0K 77K 300K

Slope Gain

x2

V(d=0)

V(d=0)


STARLightSTARLightCalibration: Warm + Hot

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

Tb=300K DSP

Delay = t

Delay = t + t

ViVq

t


STARLightSTARLightCalibration: Receiver Two-Point Cal

STAR-Light Calibration Design:Two-Point Calibration of a single channel

Trec=300K

B=20MHz =1.5 s


STARLightSTARLightCalibration: Cold Noise Source

STAR-Light Calibration Design:Quality of Cold Load

50 at 77KVSWR=1.05

L=0.3 dBVSWR=1.1

RCVR

L=0.4dBVSWR=1.1

VSWR=1.1

Phase Uncertainties:Reflection +/- 6 degTransmission +/- 12 deg


STARLightSTARLightCalibration: Correlated Noise Source

STAR-Light Calibration Design:Correlated Noise Distribution Network

3-diode design allows any one diode failure while maintaining calibration

=0.743

=0.754


STARLightSTARLightTwo Channel Prototype

Two Channel prototype tests:

•NEDT verification (Dec ’01)

•End-to-end fringe wash function measurement (Jan ’02)

•Receiver calibration validation (Feb ’02)

•Antenna radiation efficiency measurement (Spring ’02)

Tasks to be done prior to CDR:

•Antenna specification and design (Oct ’01)

•Antenna manufacture and integration (Nov ’01– Mar ’02)

•STAR model evolution (continuous)

•Cold load final design (Oct-Dec ’01)

Post CDR:

•Antenna characterization

•System validation

STAR Light PDR – 3 October 2001

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