Transcript Ultra-Wide-Band Ground Bounce Range Antenna

Digital Receiver with Interference
Suppression for Microwave Radiometry
NASA Instrument Incubator Program
Interim Review
Joel T. Johnson, Steven W. Ellingson,
Grant A. Hampson, and Nakasit Niltawach
Department of Electrical Engineering
ElectroScience Laboratory
The Ohio State University
29th April 2003
ElectroScience Lab
Outline
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Slides 1-8:
Administrative issues
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Slides 9-14:
Review basic project ideas and goals
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Slides 15-20: Recent progress/current status
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Slides 21-23: LISA
ElectroScience Lab
Instrument Incubator Program
Digital Receiver with Interference Suppression for Microwave Radiometry
ESTO
Earth Science Technology Office
PIs: Joel T. Johnson and Steven W. Ellingson, The Ohio State University
Description and Objectives
Future sea salinity and soil moisture remote
sensing missions depend critically on L-Band
microwave radiometry. RF interference is a
major problem and limits useable bandwidth to
20 MHz. An interference suppressing
radiometer could operate with a larger
bandwidth to achieve improved sensitivity and
more accurate moisture/salinity retrievals.
Approach
A prototype radiometer will be designed, built,
and used to demonstrate operation in the
presence of interference. The design includes a
processing component to suppress interference.
Co-I’s/Partners
Dr. Grant Hampson, OSU
TRL levels: from 3 to 5/6
Traditional
Radiometer
Antenna LNA Downconv. ADC Corr/Integrate
(optional)
New design
LNA
ADC
Corr/Integrate
Antenna Downconv.
RFI Processor
Schedule and Deliverables
Year 1: Complete design and begin construction
Year 2: Finish construction and begin tests
Year 3: Demonstrations and space system design
Application/Mission
Results will apply to all future microwave
radiometer missions. Future L-band soil moisture
and salinity missions are primary focus.
Project Schedule
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Project “year 1” was 9 months, 3/11/02-11/30/02
ElectroScience Lab
Progress in Year Two
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Milestone: “Progress in Breadboard Instrument Design and Algorithm
Development”
– Second backend prototype completed to achieve 100 MHz
 Two channel A/D, Digital IF, Asynchronous Pulse Blanker
(APB), FFT, Spectral Domain Processor (SDP)
– Adaptive excision algorithm used temporally in APB, spectral
implementation in SDP nearing completion
– Front end + antenna nearing completion for experiments Su 03
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Addition: LISA system flown in AMSR-E "Wakasa bay" campaign;
measured detailed L-band RFI information
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Current TRL Status: In transition from TRL 3 to TRL 4
ElectroScience Lab
Budget/Personnel
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Year 1 + Year 2 budget:533.9K + 21K equipment
Remaining as of 3/31: ~254K + 0K equipment (31.8K/month in 8 mos)
No cost under- or over-runs are expected
Tentative budget for year 3:
288.9K
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Personnel:
– J. T. Johnson, S. W. Ellingson: co-PIs
– G. A. Hampson: Research Scientist
– N. Niltawach: Graduate student (graduating June 03)
– Currently screening graduate student candidates
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Document Server (password protected):
http://esl.eng.ohio-state.edu/~swe/iip/docserv.html
ElectroScience Lab
Plans for 5/1/03-11/30/03
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5/1/03-5/31/03: “Progress in Breadboard Instrument Design and
Algorithm Development”
– Continue front and back end development
– Refine combined time domain and post-FFT processing algorithms
– Test/refine algorithms with data from LISA measurements
6/1/03-11/30/03: “Complete Breadboard Instrument Fabrication;
Progress in Laboratory Tests”
– Test complete system; study accuracy and stability (TRL 4)
– Begin outdoor tests at ESL: calibrated observations of a large
water pool (TRL 5-6)
– Refine algorithms as necessary in tests; document performance
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Annual review (ESL or GSFC?): early October 2003
– last year 10/4/02 at GSFC
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Currently proposing related work at C-band to NPOESS IPO
ElectroScience Lab
Publications
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Upcoming conference presentations Summer 2003:
– G. A. Hampson, S. W. Ellingson, and J. T. Johnson,"Design of an L-Band
Microwave Radiometer with Active Mitigation of Interference," APS/URSI
2003, Columbus.
– S.W. Ellingson, G.A. Hampson, and J.T. Johnson, "Design of an L-Band
Microwave Radiometer with Active Mitigation of Interference", NASA ESTC.
– S.W. Ellingson, G.A. Hampson, and J.T. Johnson, "Characterization of LBand RFI and Implications for Mitigation Techniques", IGARSS 2003,
Toulouse.
– S.W. Ellingson, G.A. Hampson, and J.T. Johnson, "Design of an L-Band
Microwave Radiometer with Active Mitigation of Interference", IGARSS
2003, Toulouse.
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Recent Internal reports (44 total to date)
– S.W. Ellingson and J.T. Johnson, "Airborne RFI Measurements over the
Mid-Atlantic Coast using LISA", Feb 10, 2003.
– S. Ellingson and G. Hampson, "RFI and Asynchronous Pulse Blanking at
Arecibo", Nov 12, 2002.
– J. T. Johnson and G. Hampson, "Initial Plan for a Precision Temperature
Sensor", Sep 10, 2002.
ElectroScience Lab
RFI Issues for Microwave Radiometers
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A microwave radiometer is a sensitive receiver measuring naturally
emitted thermal noise power within a specified bandwidth
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Human transmission in many bands is prohibited by international
agreement; these are the “quiet bands” ideal for radiometry
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L-band channel quiet band is 1400-1427 MHz: larger bandwidth would
improve sensitivity if RFI can be addressed. Ocean salinity missions
require extremely high sensitivity.
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Even within quiet band, RFI has still been observed - possibly due to
filter limitations or intermodulation products
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Many interferers are localized either in time or frequency: should be
relatively easy to detect and remove with an appropriate system
ElectroScience Lab
Pulsed Interferers
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Typical radiometer is a very “slow” instrument: power received is
integrated up to msec scales by analog system before being digitized
However, many RFI sources are pulsed, typically with microsecond
scale pulses repeated in millisecond scale intervals
A single microsecond scale pulse within a millisecond scale integration
period can corrupt the entire measurement
A radiometer operating a faster sampling rate has the potential to
identify and eliminate microsecond scale features without sacrificing
the vast majority of the millisecond scale data
Pulsed interferer (~msec)
Time
ElectroScience Lab
Radiometer integration period (~msec)
Example of Pulsed RFI
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Time domain (“zero span”) spectrum analyzer measurements from ESL
roof with low-gain antenna: 1331 MHz +/- 1.5 MHz
ATC radar in London, OH (43 km away): PRF 350 Hz, 2 usec pulses
plus multipath, approximate 10 sec rotational period
ElectroScience Lab
Narrow-band Interferers
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Typical radiometer also has a single, large bandwidth channel (20 MHz
or more): total power within this channel is measured
However, many RFI sources are narrow-band (<=1MHz),
Again, a single 1 MHz interferer within the channel can corrupt the
entire measurement
A radiometer operating with many much smaller channels has the
potential to identify and eliminate narrowband interferers without
sacrificing the vast majority of the bandwidth
Narrowband interferer (~1 MHz)
Frequency
ElectroScience Lab
Radiometer channel bandwidth (~100 MHz)
System Block Diagram
Antenna
Low-noise
front end
Asynchronous Pulse
Blanker
Analog
Downconverter
1024 point FFT
Integration
ElectroScience Lab
ADC
Digital
Downconverter
Frequency domain
blanker
Data Recording/
Control
Initial Results: Time Blanking of ATC Radar
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Time domain results:
Direct path Multi-path?
APB “Blanking”
decision
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Effect of varying APB threshold in frequency domain:
“Max held” spectra
Averaged spectra
ElectroScience Lab
Initial Results: Blanking a Dual Frequency Radar
at Arecibo using the IIP Digital Receiver
The radio telescope at Arecibo, PR suffers
from RFI from distant ground-based air search
radars
1325-1375 MHz spectra including digital IF,
APB, FFT, and integration (42 msec)
Before: ATC radar pulses visible
ElectroScience Lab
After: APB removes radar
Radiometer Front End/Downconverter
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Relatively standard super-het design: expected Tsys approx. 400K
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100 MHz split into two back-end channels due to ADC limits
Stability: analog gain reduced by high dynamic range ADC, low order
analog filters, internal cal loads
Temperature sensing of terminator, thermal control components
functioning
Final implementation awaiting integration with system antenna
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ElectroScience Lab
Digital Back-End
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System design includes digital IF downconverter (DIF), asynchronous
pulse blanker (APB), FFT stage, and SDP operations
Analog
Devices
9410
ADC
DIF
APB
FFT
SDP
ADC
200 MSPS
100 MSPS I/Q
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Most blocks on separate boards to simplify testing and reconfiguration
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Microcontroller interface via ethernet for setting on-chip parameters
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Second prototype uses Altera "Stratix" FPGA’s: apprx 10000 LE, $260
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Designs for all components complete; DIF, APB, FFT, SDP, and
capture card initial implementations functioning
ElectroScience Lab
Current Digital Back-End Implementation
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Modular form used for processor boards: note microcontrollers
EEPROM's on each card for autoprogramming of FPGA's on power-up
ADC
DIF/
APB
ADC
ElectroScience Lab
FFT
SDP
Capture
Interference Suppression Algorithms
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APB updates mean/variance of incoming time domain signal; a sample
> b standard deviations above the mean triggers blanker
Blanking operates on down-stream data exiting a FIFO; blank signals
before and after blanking trigger
Parameters: blanking window size, precursor length, threshhold
With multiple “blanking timing registers” (BTRs), additional “pulses”
occurring during blanking window can trigger more blanking events
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Post-FFT: two methods
– similar to APB, monitor per-bin mean/variance in time and blank
outliers
– unlike APB, can also blank outliers in freq. response at single time
– window lengths and thresholds to be quantified in future work
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Parametric: remove interferer based on parametric fit to a specific
functional form; to be explored further in future work
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Calibration effects corrected in real-time by appropriate scale factors
ElectroScience Lab
Experiment Planning
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A series of experiments with the prototype will be conducted at ESL
beginning Su 03
Observations of a large water tank; external cal sources are ambient
absorbers and a sky reflector
Initial tests in existing RFI; artificial RFI to be added as tests progress
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Antenna mount completed, front end box to be integrated with feed
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Height (m)
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ElectroScience Lab
LISA: L-Band Interference Surveyor/Analyzer
S.W. Ellingson, J.T. Johnson, and G.A. Hampson, The Ohio State University
Nadir-looking
cavity-backed spiral
antenna w/ custom LNA
& calibration electronics
in tail radome
RF distribution,
antenna unit control &
coherent sampling
subsystem
LISA co-observes with existing
passive microwave sensors to
identify sources of damaging
radio frequency interference
(RFI)
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1200-1700 MHz using
broadbeam spiral antenna
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Spectrum analyzer for fullbandwidth monitoring of power
spectral density
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14 MHz (8+8 bit @ 20 MSPS)
coherent sampling capability for
waveform capture and analysis
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Flexible script command
language for system control &
experiment automation
Spectrum analyzer,
electronics rack &
control console
mounted in cabin
NASA’s P-3 Orion Research Aircraft
Maiden LISA Flight: January 2, 2003 from Wallops Island, VA
Examples of RFI observed at 20,000 feet
LISA Wakasa Bay Campaign
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Date
LISA was deployed in the AMSR-E "Wakasa Bay" cal-val campaign;
thanks to E. Kim and R. Austin (Co. State) for operations
Antenna in P-3 radome: high loss decreased sensitivity
On board, permanent RFI for frequencies <~1320 MHz
Problems with receiver compression in many cases; high loss helped!
Some software/control issues resulted in a few cases of data loss
Description
# of files
“Pulses”
1/2
1/3
1/4
Wallops test flight
Wallops to Monterey
Monterey to Kona
615
4372
1616
1.79%
1.85%
0.06%
1/6
Wake to Japan
5287
0.15%
1/14
Sea of Japan
3987
1.58%
1/15
W. Japan
2342
2.04%
1/19
W Pacific
78
0.00%
1/21
W Pacific
2480
0.00%
1/23
W Pacific
3643
2.25%
1/26
W Japan
1033
1.45%
1/28
Sea of Japan
3212
1.00%
1/29
Sea of Japan
3421
2.22%
1/30
Sea of Japan
3824
2.01%
W Japan
1870
1.39%
37165
509
2/1
Total
ElectroScience Lab
LISA Initial Results Summary
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Campaign produced 8 GB of data: initial software developed to autodetect large "pulses" > 200 stds above mean
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Results sorted manually to find interferers localized in time/frequency
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Analysis continues for other types and weaker amplitude interferers
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Detailed examination of 1411-1425 MHz channel shows numerous
triggers, but signal properties are difficult to classify
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Captures useful for testing effectiveness of suppression algorithms
ElectroScience Lab