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Designing a Broadband Polarizer for the SZA Without any Heavy Lifting

Designing a Broadband Polarizer for the SZA Without any Heavy Lifting. Matthew Sharp March 10, 2004. Why Polarize?. Telescope Calibration: requires observation of point sources These tend to be linearly polarized at 10% level Rotation of earth introduces a modulation in this signal

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Designing a Broadband Polarizer for the SZA Without any Heavy Lifting

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  1. Designing a Broadband Polarizer for the SZA Without any Heavy Lifting Matthew Sharp March 10, 2004

  2. Why Polarize? • Telescope Calibration: • requires observation of point sources • These tend to be linearly polarized at 10% level • Rotation of earth introduces a modulation in this signal • Measuring circular polarization signal instead eliminates this modulation

  3. 1 2 1 2 1 2 What a Polarizer Does: • Linear-to-Circular Polarizer retards one mode 90º more than the other two orthogonal modes in waveguide (both are propagating out of the page) Circular Polarization: one mode’s wave is lagging behind the other by 90º Linear Polarization: Waves in two modes are in phase

  4. b Propagation Constant (effective wave number in dielectric): B=(em*w2+kc2)1/2 Df~bx-by dielectric geometry w Things that Polarize: Dielectric Slab

  5. Corrugations change both geometry and effective dielectric constant-can form a polarizer which is very achromatic

  6. Simulations with HFSS

  7. Waveguide Sanity Test: Compare to test results… S21 dB HFSS

  8. Corrugation Polarizer Df

  9. Scaling a design to 90Ghz Df

  10. Multiple Elements Multiple elements can be combined linearly to cancel frequency variations

  11. 2-element Polarizers: • The Game Begins-try to tweak parameters to find maximum flatness in region of interest • Can play with: • All lengths of corrugations • Angles between corrugations

  12. By changing orientation of sections, can make the response flat…

  13. By changing length of sections, can tune response higher and lower…

  14. But in the Real World… In principle, the polarizer we want can be created by lengthening the corrugation sections of a flat result…. • but there are practical considerations: • Can it actually be built? • Can it fit in the existing cryostat?

  15. Should redo with axes Stacking the sections on top of each other produces different results…hopefully this has promise!

  16. Coming Next: • Finalize a design • Build and test a scaled version at 30GHz • Redesign, if necessary • Build and test 90 GHz models • Install!

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