Transcript Ultra-Wide-Band Ground Bounce Range Antenna

Digital Receiver with Interference
Suppression for Microwave Radiometry
NASA Instrument Incubator Program
Year 2 Annual Review
Joel T. Johnson, Steven W. Ellingson*,
and Grant A. Hampson
Department of Electrical Engineering
ElectroScience Laboratory
The Ohio State University
*Department of Electrical and Computer Engineering
Virginia Tech
28th October 2003
ElectroScience Lab
Outline

Slides 1-8:
Administrative issues

Slides 9-17:
System development

Slides 18-23: Progress in experiments

Slides 24-26: 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. Corr/
ADC
(optional) integrate
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

Project “year 1” was 9 months, 3/11/02-11/30/02
ElectroScience Lab
Progress in Year Two

Current Milestone: “Complete Breadboard Instrument Fabrication;
Progress in Laboratory Tests”
– Dual channel 100 MHz system completed (second prototype)
– Temporal blanking strategy updated; progress in software RFI
processor
– Antenna, front end, downconverter integration complete
– Experiments currently in progress

Addition: LISA system flown in AMSR-E "Wakasa bay" campaign;
measured detailed L-band RFI information

Current TRL Status: In transition from TRL 3 to TRL 4
ElectroScience Lab
Budget/Personnel




Year 1 + Year 2 budget:533.9K + 21K equipment
Remaining as of 9/30: ~50K + 0K equipment (25K/month in 2 mos)
No cost under- or over-runs are expected
Tentative budget for year 3:
288.9K

Personnel:
– Co-Pis: J. T. Johnson, S. W. Ellingson
– Lead Designer (Research Scientist): G. A. Hampson
– RF Support (Research Scientist): Chi-Chih Chen
– Technician: Jim Moncrief, Ray Feast
– Graduate Students: Nakasit Niltawach (Graduated June 03),
Al
Hayslip (Graduated June 03), Noppasin Niamsuwan,
Ranga
Krisnamurchi
– Undergrads: Mark Frankford, Ben Sinsheimer, Ryan Schultz,
Miguel Lafleche

Document Server (password protected):
http://esl.eng.ohio-state.edu/~swe/iip/docserv.html
ElectroScience Lab
Plans for 12/1/03-11/30/04

12/1/03-11/30/04: “Studies of space deployment and advanced
algorithms; Larger scale observations”
– Continue experiments to refine suppression algorithms
– Perform tests in artificially generated RFI environments
– Test/refine algorithms with data from LISA measurements
– Develop basic design for space-borne system

Interim telecon review: April-May 2004
– last year 4/29/03

Project supported by NPOESS IPO on use of system at C-band is
currently in progress; recent briefing on project to Boeing Satellite
Systems/IPO/Aerospace

First flight at C-band estimated as Spring 2004

We’re interested in discussing possibilities for continuation of this work
beyond this IIP project
ElectroScience Lab
Publications
Recent Conference Presentations:
– 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.
– G. A. Hampson, S. W. Ellingson, and J. T. Johnson, “Design and
Demonstration of an interference suppressing microwave radiometer,”
submitted to IEEE Aerospace Conference, 2004.

Recent Internal Reports:
– J. T. Johnson and S. W. Ellingson, “Airborne RFI Measurements using LISA
during transit to and in the Wakasa Bay Campaign,” July 7, 2003.
– S.W. Ellingson and J.T. Johnson, "Airborne RFI Measurements over the
Mid-Atlantic Coast using LISA", Feb 10, 2003.
ElectroScience Lab
RFI Issues for Microwave Radiometers

A microwave radiometer is a sensitive receiver measuring naturally
emitted thermal noise power within a specified bandwidth

Human transmission in many bands is prohibited by international
agreement; these are the “quiet bands” ideal for radiometry

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.

Even within quiet band, RFI has still been observed - possibly due to
filter limitations or intermodulation products

Many interferers are localized either in time or frequency: should be
relatively easy to detect and remove with an appropriate system
ElectroScience Lab
System Overview





Typical radiometer is a very “slow” instrument: power received is
integrated up to msec scales by analog system before being digitized
Typical radiometer has a single, large bandwidth channel: susceptible
to narrow band interference
Our design uses a digital receiver to allow much more rapid sampling
of incoming data; this rapid sampling improves the ability to mitigate
temporally localized RFI
Our design also performs a 1024 point FFT operation; improves ability
to mitigate spectrally localized RFI
Processor must operate in real time so that final data rate can be
reduced to a manageable level; implement processor in hardware
(FPGA’s)
Pulsed interferer (~msec)
Radiometer integration period (~msec)
ElectroScience Lab
Time
System Block Diagram
Antenna
Low-noise
front end
Asynchronous Pulse
Blanker
Analog
Downconverter
ADC
1024 point FFT
Digital
Downconverter
Frequency domain
blanker
(not yet implemented)
Integration
ElectroScience Lab
Data Recording/
Control
Digital Back-End

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

Dual channel implementation completed

Most blocks on separate boards to simplify testing and reconfiguration

Microcontroller interface via ethernet for setting on-chip parameters

Second prototype uses Altera "Stratix" FPGA’s: apprx 10000 LE, $260

Designs for all components complete; DIF, APB, FFT, SDP, and
capture card initial implementations functioning
ElectroScience Lab
Current Digital Back-End Implementation


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
Improved APB algorithm


APB updates mean/variance of incoming time domain signal; a sample
> b standard deviations above the mean triggers blanker
Previous design had only one “blanking timing register” (BTR); no
detection of pulses with a blanking operation in progress
NBLANK
NWAIT
Threshold
NSEP


New design (green curves) has multiple BTR’s so pulse detection
always possible; detections must be separated by NSEP
Calibration effects to be corrected in real-time by appropriate scale
factors
ElectroScience Lab
Spectral Domain RFI Processing

A per-bin time domain blanking strategy similar to the APB can be
implemented in the SDP component; higher SNR for better blanking

Cross frequency algorithms currently under investigation; basic idea is
to search for regions of rapid change in spectrum

Testing these in software at the moment using integrated data;
immense amount of data generated at full sample rate makes full test
problematic

For true CW interferers, rapid temporal processing is not necessary;
software scheme to throw out corrupted bins would be fine

Similar to algorithms used for analog sub-band radiometers (e.g. PSR
C-band system)

Digital receiver gives capability of obtaining a large number of bins
(here 1024) as opposed to only a few with analog sub-channels
ElectroScience Lab
Antenna/Front End Unit

Front end Tsys approx. 200K neglecting antenna
Temperature control is
critical to maintain internal
standards; rest of system not
temperature controlled
Still experimenting with
overall system stability
ElectroScience Lab
Dual Channel Downconverter

One channel is ~1325-1375 MHz, other is ~1375-1425 MHz

Downconverter, digital receiver, computer, and thermal control systems
in rack inside lab
Working with system gain ~70 dB at present: moves –94 dBm in 100
MHz to –24 dBm; this triggers 4-5 ADC bits

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
Experiments at OSU



Height (m)

Experiments designed to demonstrate radiometric accuracy in the
presence of interference
Observations of a large water tank; external cal sources are ambient
absorbers and a sky reflector
Highly accurate ground-based radiometry is tough due to contributions
from objects not under view, including reflections
Keep cal targets exactly the same size as pool to reduce these effects;
observations of pool as ambient temp varies also

Initial tests in existing RFI; artificial RFI to be added as tests progress
ElectroScience Lab
Pool and Cal Targets




Water pool is approximately 16’ x 32’ by 6” deep; use saline water to
decrease skin depth and eliminate sub-pool contributions
Absorbers are 12” (a few 18”) to cover the area; mounted on “racks”
that can be placed on pool by a team of 2-4 people
Reflectors are foil covered foam
Temperature of pool, absorbers, and ground around pool all recorded;
salinity of pool checked for each experiment
ElectroScience Lab
Pool and Cal Targets
Absorbers: Assume Tb=Tphys
Reflectors: Assume Tb=Tref~Tsky?
Water: Tb~Twat+QTref
Possible background
contributions make precise
calibration tough; data analysis
to sort out these effects currently
in progress
ElectroScience Lab
Results: System Stability

Observation of internal loads for approximately 10 hours; total power
measurement, no RFI suppression

Gain varies appreciably for internal loads, due to uncontrolled cable
and downconverter stages
Terminator result can be stabilized to <~0.01 dB over 10 hours through
use of internal loads
Front end temperature controller still has 0.2K variation, plus strange
0.5K step; improvements here may improve stabilize further


ElectroScience Lab
Current Experiment Results

Hardware integration period 21 msec, switched every 1.33 secs
through front end states, every 5 seconds through receiver mode
Horizontally polarized
data, absorber observation
Radar at 1331 MHz
apparent, along with
other more CW RFI
Blanker reduces radar
effects, as well as
saturation problems in
FFT computation
ElectroScience Lab
Initial Calibrated Brightnesses

Initial results of experiment show promise, although spectral features
needing correction are apparent; data shown includes software blanker
RFI contributions
still corrupt measurement
even with blanker on
Results with blanker off
are similar, but further
from model
Real interest here is
total power radiometry;
need good spectral
blanker for this
Data at higher sample
rate will improve software
RFI suppression
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)

1200-1700 MHz using
broadbeam spiral antenna

Spectrum analyzer for fullbandwidth monitoring of power
spectral density

14 MHz (8+8 bit @ 20 MSPS)
coherent sampling capability for
waveform capture and analysis

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





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 Results Summary

Campaign produced 8 GB of data: initial software developed to autodetect large "pulses" > 200 stds above mean

Results sorted manually to find interferers localized in time/frequency

Numerous ARSR systems observed both in Japan and US; can
correlate data versus ARSR position to examine range effects

Other radars also observed: chirped, varying pulse widths, multiple
frequencies, etc.

Japanese data show some wideband channels, also a satellite
downlink (1698 MHz); tests with these will challenge simple
suppression algorithms

Detailed examination of 1411-1425 MHz channel shows numerous
triggers, but signal properties are difficult to classify

Captures useful for testing effectiveness of suppression algorithms; will
be used in space system design evaluation
ElectroScience Lab