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Chaff RCS Modelling

Chaff RCS Modelling. By Neil Kruger Supervisor: Prof. KD Palmer University of Stellenbosch. Introduction. Chaff Background Dipole RCS Dipole Spatial Average RCS Chaff Cloud RCS Screening Effect of Chaff GUI Tool Summary. Chaff Background.

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Chaff RCS Modelling

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  1. Chaff RCS Modelling By Neil Kruger Supervisor: Prof. KD Palmer University of Stellenbosch

  2. Introduction • Chaff Background • Dipole RCS • Dipole Spatial Average RCS • Chaff Cloud RCS • Screening Effect of Chaff • GUI Tool • Summary © CSIR 2006 www.csir.co.za

  3. Chaff Background • Chaff consist of very thin dipoles cut to resonant length • With different cut lengths a larger radar bandwidth can be covered • Dispensed in the atmosphere to form a cloud of scatterers • Dispensed by dropping or firing from ships or aircraft. • Chaff can be used in different missions, but overall the purpose of chaff is to mask the radar target © CSIR 2006 www.csir.co.za

  4. Dipole RCS- Single Dipole Orientation • Numerous factors influence the RCS a chaff cloud • To model a chaff cloud as a whole, one first needs to understand the RCS behavior of a single dipole element • This initial investigation was done analytically © CSIR 2006 www.csir.co.za

  5. Dipole RCS -Analytical Model © CSIR 2006 www.csir.co.za

  6. Dipole Single Orientation RCS - Analytical Results vs. FEKO © CSIR 2006 www.csir.co.za

  7. Dipole Single Orientation RCS - Analytical Results with Error Correction © CSIR 2006 www.csir.co.za

  8. Dipole Spatial Average RCS • The RCS of a dipole can be calculated for any orientation, but this is limited to the resonant frequency. • Literature addressing this problem by O. Einarsson is available • The original Einarsson paper was obtainable but a revised paper was not, so it was decided to direct the modeling approach from a analytical to a computational approach. © CSIR 2006 www.csir.co.za

  9. Dipole Spatial Average RCS- Literature • From literature the average value was found to differ between 0.15λ² and 0.28λ² depending on approach used. • Further literature study grouped these values as below • 0.15λ² - 0.17λ² for a dipole uniformly distributed over a sphere • 0.27λ² - 0.29λ² for a dipole uniformly distributed over a disc • 0.22λ² is the value associated with the Scattering Cross Section • For SCS the polarization is not taken into account © CSIR 2006 www.csir.co.za

  10. Dipole Spatial Average RCS- Dipole Bistatic Spatial Average RCS at Resonance © CSIR 2006 www.csir.co.za

  11. Dipole Spatial Average RCS- Results © CSIR 2006 www.csir.co.za

  12. Dipole Spatial Average RCS- Results © CSIR 2006 www.csir.co.za

  13. Chaff Cloud RCS • The next step is modeling the RCS of a chaff cloud. • Simple mathematical equations exist to address this problem analytically. • These equations are however limited to dipoles at resonance • The chaff cloud modeling needs to be investigated computationally. © CSIR 2006 www.csir.co.za

  14. Chaff Cloud RCS- Back Scatter RCS • Simple relationship exists for calculating the backscatter RCS of a chaff cloud: • This simple equation is well known for sparsely spaced chaff clouds with negligible inter-dipole coupling and will the formulation will not be discussed © CSIR 2006 www.csir.co.za

  15. Chaff Cloud RCS- Hypothesis for Forward Scatter RCS • A relationship exists between the forward scatter RCS (being coherent) and the number of dipoles, such that the forward scatter RCS is directly proportional to N²: © CSIR 2006 www.csir.co.za

  16. Chaff Cloud RCS - Modeling a Chaff Cloud Creating a sphere of randomly orientated and uniformly distributed dipoles © CSIR 2006 www.csir.co.za

  17. Chaff Cloud RCS - Modelling a Chaff Cloud • A 1m³ spherical chaff cloud was simulated with an increasing dipole density, to compare analytical and computational back scatter results • Results were averaged over 15 simulations to determine a statistical average • The forward scatter RCS was also averaged and the proportional constant was derived as k = 0.07 © CSIR 2006 www.csir.co.za

  18. Chaff Cloud RCS - Average RCS Plot over 15 Simulations © CSIR 2006 www.csir.co.za

  19. Chaff Cloud RCS - Forward Scatter and Back Scatter Results • Simulations results coincide within 2dB from Analytical results © CSIR 2006 www.csir.co.za

  20. Chaff Cloud RCS - Coupling © CSIR 2006 www.csir.co.za

  21. Chaff Cloud RCS - Coupling These values serve as guidelines for applying the analytical formulation © CSIR 2006 www.csir.co.za

  22. Screening effect of Sparse Clouds • Chaff’s primary application is as a military defense mechanism to avoid detection or attack by adversary defense systems. • A chaff cloud forms the EM equivalent of a visual smoke screen that can temporarily hide the target from radar. • This is known as the screening effect of chaff or “shadowing” and will be discussed. © CSIR 2006 www.csir.co.za

  23. Screening effect of Sparse Clouds- Hypothesis • A relationship exists between the forward scattering of a chaff cloud and that of a solid sphere so that the E-field behind the cloud can be modeled in terms of this relationship: • The formulation of the hypothesis will be explained at the hand of the following figures… © CSIR 2006 www.csir.co.za

  24. Screening effect of Sparse Clouds- Hypothesis © CSIR 2006 www.csir.co.za

  25. Screening effect of Sparse Clouds- Hypothesis © CSIR 2006 www.csir.co.za

  26. Screening effect of Sparse Clouds- Hypothesis © CSIR 2006 www.csir.co.za

  27. Screening effect of Sparse Clouds- Hypothesis © CSIR 2006 www.csir.co.za

  28. Screening effect of Sparse Clouds- Initial Simulation © CSIR 2006 www.csir.co.za

  29. Screening effect of Sparse Clouds- Initial Simulation Results © CSIR 2006 www.csir.co.za

  30. Screening effect of Sparse Clouds- Simulation investigating the Hypothesis © CSIR 2006 www.csir.co.za

  31. Screening effect of Sparse Clouds- Near field results for increasing N and constant density © CSIR 2006 www.csir.co.za

  32. Screening effect of Sparse Clouds- Proportional constants © CSIR 2006 www.csir.co.za

  33. Screening effect of Sparse Clouds- Near field results for increasing N and increasing density © CSIR 2006 www.csir.co.za

  34. Screening effect of Sparse Clouds- Near field results at high densities © CSIR 2006 www.csir.co.za

  35. Screening effect of Sparse Clouds- Near field results vs. Hypothesis © CSIR 2006 www.csir.co.za

  36. Screening effect of Sparse Clouds- Near field results vs. Hypothesis © CSIR 2006 www.csir.co.za

  37. Screening effect of Sparse Clouds- Conclusion • It is thus possible to accurately model the near field behavior of a chaff cloud on small scale • This is however limited to low density chaff clouds at resonance • Further investigation and modeling is still possible © CSIR 2006 www.csir.co.za

  38. GUI Tool • Demo © CSIR 2006 www.csir.co.za

  39. Summary © CSIR 2006 www.csir.co.za

  40. Screening RCS Theory + Corr. Term Theory + Postulate σforward,f0 σavg,f0 c σavg, 0.05-20GHz Postulate screening, f0 σcloud GUI

  41. Questions?

  42. © CSIR 2006 www.csir.co.za

  43. © CSIR 2006 www.csir.co.za

  44. GUI Tool © CSIR 2006 www.csir.co.za

  45. GUI Tool © CSIR 2006 www.csir.co.za

  46. GUI Tool © CSIR 2006 www.csir.co.za

  47. GUI Tool © CSIR 2006 www.csir.co.za

  48. GUI Tool © CSIR 2006 www.csir.co.za

  49. GUI Tool © CSIR 2006 www.csir.co.za

  50. GUI Tool © CSIR 2006 www.csir.co.za

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