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Physical Scintillation Simulation. Diffraction Grating-Based GPS Physical Scintillation Simulation Results. Kirtland AFB, NM 19 June2012. Dr. Todd Pedersen Capt. Melanie Huffman Mr. R . Todd Parris AFRL, Space Vehicles Directorate, Kirtland AFB, NM.

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Physical scintillation simulation
Physical Scintillation Simulation

Diffraction Grating-Based

GPS Physical Scintillation Simulation Results

Kirtland AFB, NM

19 June2012

Dr. Todd Pedersen Capt. Melanie Huffman

Mr. R. Todd Parris

AFRL, Space Vehicles Directorate, Kirtland AFB, NM

Attempt to simulate ionospheric scintillation and nav outages by physically altering live GPS signal

2-D L-band diffraction gratings created out of metallic wire “field fence” with holes 12” wide by 4”-12” high (graduated spacing, wide at top, narrow at bottom)

One curved panel approx 6’ long

One cylinder approx 3’ diameter x 4.5’ high

Waved over antenna on rooftop

2 Ashtech Z-12 receivers connected to same antenna via splitter

Test of receiver-specific effects or power level discrepancies

Experiment Setup

Courtesy of C. Mitchell


  • 5 variations: panel only, cylinder only, cylinder topped with panel, cylinder+panel+foam board with metallic tape, 4 metallic tape foam boards in box configuration

Cylinder only

Topped with panel

Foam board added


  • 2 Ashtech Z-12 receivers

    • S/N 04299 Firmware 1L00-1D04

    • S/N 03789 Firmware 1L00-1D04

    • Data collection by GPS-SCINDA Version 1.77 on both

  • Splitter with DC bias to pre-amp powered by RX # 03789

Test timeline
Test Timeline

19:31 UT Antenna connected

19:36 UT “Scintillation” commencement (single flat grating)

19:40 UT Cylindrical grating

19:44 UT Cylinder plus grating on top

19:50 UT Break

19:54 UT Foam board added under top grating

19:57 UT Added foam “wings”

20:01 UT Back to baseline

20:06 UT Foam blockers only

20:10 UT Foam blockers in “box” formation ~24” above

20:15 UT Attempt to produce maximum impact (rapid movement)

20:20 UT End of “scintillation”

20:25 UT Pack up

Positioning errors first half of test
Positioning ErrorsFirst Half of Test

  • Identical receivers on same antenna

  • One has no outages, the other >6 min at a time

Some Errors and Extensive Outages

Some Errors but No Outages

Positioning errors second half of test
Positioning ErrorsSecond Half of Test

  • More severe portion of test (diffraction+blocking)

  • Some similarity in error patterns, but total outage length differs by > 10x

Fluctuations on individual links
Fluctuations on Individual Links


  • More similarity in gaps on individual links

  • Absolute signal levels in close agreement



Mesh Panel

Mesh Cylinder

Panel over Cylinder

Added Foam


Comparison of l1 and l2 amplitudes
Comparison of L1 and L2 Amplitudes

RX 04299

  • L2 drops out more frequently

  • Dispersion effects?-- more amplitude loss at L2?

  • Grating is more reflective at L2 than at L1


Loss of codeless tracking?


Highest elevation satellite l1
Highest Elevation Satellite—L1

  • Mean signal level appears to be unchanged from background with wire mesh only

RX 03789

RX 04299

Highest elevation satellite l2
Highest Elevation Satellite—L2

  • Clear difference in signal levels from cylinder and overhead panel

  • Much less than amplitude drops from foam board

RX 03789

RX 04299


  • Transmission grating-based scintillation simulation successful

    • Clear difference between L1 and L2 effects, significant loss-of-lock and navigation outages

    • Only minor reduction in amplitude compared to foil tape

    • Greater distance from antenna may provide even better performance (far field instead of near field)

  • Positioning outages extremely receiver-dependent

    • Identical receivers, identical firmware, same antenna, 10X difference in outage length

  • Should use as many receivers as practical with simulator to get a feel for unit-specific characteristics and statistical range for each receiver type

    • Test with single unit may be very misleading/atypical