Dipole Antenna

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A dipole antenna is the simplest antenna but its radiation characteristics are very good. The main drawback of a dipole antenna is very narrow bandwidth. The analysis of a dipole antenna can be performed with integration of Hertzian dipoles.

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Dipole Antenna

  1. 1. Antenna Engineering CHO, Yong Heui Dipole Antenna
  2. 2. Half-wave dipole antenna 1. Dipole antenna <ul><li>Current approximation </li></ul> Balun Coaxial cable Dipole antenna
  3. 3. Principle 1. Dipole antenna
  4. 4. Electric field <ul><li>Integration of Hertzian dipole </li></ul> 1. Dipole antenna
  5. 5. Far-field vs. Fourier transform <ul><li>Radiation pattern: Fourier transform of source current with respect to wavenumber </li></ul> 1. Dipole antenna
  6. 6. <ul><li>Directivity </li></ul>Radiation pattern 1. Dipole antenna 
  7. 7. <ul><li>Radiation pattern: </li></ul>Dipole antenna with length L 1. Dipole antenna 
  8. 8. <ul><li>Antenna length </li></ul><ul><li>Mainlobe, sidelobe, backlobe, and null </li></ul><ul><li>Broadside and end-fire antenna </li></ul>Radiation pattern 1. Dipole antenna  L = 0.5, 1, 1.5 L = 2, 2.5, 3
  9. 9. <ul><li>Radiation resistance </li></ul>Radiated power 1. Dipole antenna 
  10. 10. <ul><li>Radiation resistance </li></ul>Half-wave dipole antenna 1. Dipole antenna  
  11. 11. <ul><li>Directivity </li></ul>Half-wave dipole antenna 1. Dipole antenna  
  12. 12. <ul><li>Inductive loading: input </li></ul><ul><li>Top loading, L-shaped antenna </li></ul><ul><li>Pig-tail antenna </li></ul><ul><li>Narrow bandwidth </li></ul><ul><ul><li>10dB return loss or VSWR 2:1 </li></ul></ul>Characteristics of half-wave dipole 1. Dipole antenna 
  13. 13. <ul><li>Coaxial line </li></ul><ul><li>Quarter-wave dipole with ground </li></ul><ul><li>Image theorem </li></ul><ul><li>Sleeve monopole </li></ul>Characteristics 2. Monopole antenna 
  14. 14. Monopole vs. dipole 2. Monopole antenna 
  15. 15. Design of monopole antenna 2. Monopole antenna Courtesy to www.freeuk.com  Monopole Connector Transition
  16. 16. <ul><li>Tilted dipole antenna </li></ul><ul><li>High directivity </li></ul><ul><li>Easy beam scanning </li></ul>Characteristics 3. Vee dipole 
  17. 17. <ul><li>Transmission line mode </li></ul><ul><li>Antenna mode </li></ul>Characteristics 4. Folded dipole 
  18. 18. <ul><li>: infinity </li></ul><ul><li>Real input impedance: resonance </li></ul>Half-wave folded dipole 4. Folded dipole  
  19. 19. <ul><li>Feeding: maximum current </li></ul><ul><li>Balun (Balanced to Unbalanced) </li></ul><ul><ul><li>Coaxial cable </li></ul></ul><ul><ul><li>Sleeve balun (bazooka balun) </li></ul></ul>Balun 5. Feeding 
  20. 20. <ul><li>Coaxial line to folded dipole </li></ul><ul><li>Current division and voltage doubling </li></ul><ul><li>Ferrite core: transformer </li></ul>1:4 balun 5. Feeding 
  21. 21. Chu limit 6. Antenna limit

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