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Single Dish Radio Telescopes and Radiometers: Exploring the Cosmos

Learn about radio telescopes, antennas, electromagnetic radiation, and more at the Single Dish School 2015. Gain insights into antenna operations, patterns, and instruments used in radio astronomy. Discover topics such as the reciprocity theorem, antenna technology, and spectrometers for studying celestial objects. Visit the National Radio Astronomy Observatory website for further information.

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Single Dish Radio Telescopes and Radiometers: Exploring the Cosmos

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  1. Radio Telescopes and Radiometers 2015 Single Dish School Jim Condon NRAO, Charlottesville

  2. Radio Telescopes and Antennas • An antenna is any device that converts electromagnetic radiation traveling through space to electrical currents flowing in a wire (receiving antenna) or vice-versa (transmitting antenna). • Radio telescopes, and only radio telescopes, contain antennas. • Most of a typical radio telescope is not an antenna − the big dish just redirects electromagnetic radiation to the antenna part. Single Dish School 2015 July 6

  3. Electromagnetic radiation is produced by accelerating charged particles Single Dish School 2015 July 6

  4. Dipole antenna Power pattern Single Dish School 2015 July 6

  5. Reciprocity theorem  The receiving and transmitting patterns of an antenna are identical. Single Dish School 2015 July 6

  6. Ground-plane Waveguide horn vertical = ½ of a half-wave dipole Single Dish School 2015 July 6

  7. The waveguide horn used to discover λ = 21 cm HI emission from our Galaxy Single Dish School 2015 July 6

  8. Parabolic reflector:directivity and collecting area Prime focus Single Dish School 2015 July 6

  9. Aperture Single Dish School 2015 July 6

  10. Illumination, field, and power patterns Single Dish School 2015 July 6

  11. Cassegrain subreflector Single Dish School 2015 July 6

  12. 140-foot (43 m)Cassegrain Single Dish School 2015 July 6

  13. Reflector surface errors Single Dish School 2015 July 6

  14. 100 m homology telescope in Effelsberg Single Dish School 2015 July 6

  15. GBT: homology plus active surface Single Dish School 2015 July 6

  16. GBT Offset Gregorian + Prime Focusfor unblocked aperture Single Dish School 2015 July 6

  17. Single Dish School 2015 July 6

  18. GBT feeds andradiometers Single Dish School 2015 July 6

  19. Antenna output noise: voltage and power TA = “antenna temperature” Ae = effective area S = flux density Pν = power per unit frequency k = Boltzmann’s constant ≈ 1.38 × 10−23 Joules per Kelvin Single Dish School 2015 July 6

  20. The simplest radiometer Single Dish School 2015 July 6

  21. Square-law detector: output noise voltage is proportional to input power Single Dish School 2015 July 6

  22. Integrator output noise for: N = 50 samples N = 200 samples Single Dish School 2015 July 6

  23. Differential radiometer Single Dish School 2015 July 6

  24. Superheterodyne receiver Single Dish School 2015 July 6

  25. Spectrometers and software-defined digital back ends  Single Dish School 2015 July 6

  26. To learn more about radio astronomy, Google Essential Radio Astronomy http://www.cv.nrao.edu/course/astr534/ERA.shtml or see the printed book (4 copies are on reserve) The National Radio Astronomy Observatory is a facility of the National Science Foundationoperated under cooperative agreement by Associated Universities, Inc. Single Dish School 2015 July 6

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