Loop Antenna

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A loop antenna has simple structure but its analysis is not easy to perform. Since a loop antenna is a dual pair of a dipole antenna, we can adopt the analysis of a dipole for a loop based on the duality theorem. By stacking a number of loops, we can increase the antenna gain and radiation resistance very easily.

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Loop Antenna

  1. 1. Antenna Engineering CHO, Yong Heui Loop Antenna
  2. 2. Small loop antenna 1. Loop antenna <ul><li>Duality theorem </li></ul><ul><li>Electric dipole antenna </li></ul> 
  3. 3. Magnetic dipole moment 1. Loop antenna <ul><li>Electric dipole moment vs. magnetic dipole moment </li></ul> 
  4. 4. Near field components 1. Loop antenna <ul><li>Constant current </li></ul><ul><li>Duality theorem: </li></ul>
  5. 5. Far field components 1. Loop antenna <ul><li>Observation point: infinity </li></ul>
  6. 6. Radiation power and resistance 1. Loop antenna <ul><li>Effective antenna: # of turns </li></ul>  Single turn Multiple turns
  7. 7. Loop-stick antenna 1. Loop antenna <ul><li>Ferrite core and multiple turns </li></ul><ul><li>Large radiation resistance </li></ul><ul><li>AM receiver </li></ul>
  8. 8. One-wavelength loop antenna 1. Loop antenna <ul><li>Continuous current distribution </li></ul><ul><ul><li>Not uniform current </li></ul></ul><ul><ul><li>Compared with standing wave antenna </li></ul></ul><ul><ul><li>Traveling wave antenna </li></ul></ul><ul><li>Square loop antenna: gain = 3.09 dB </li></ul>
  9. 9. Crystal loop antenna 1. Loop antenna <ul><li>Efficient antenna: multiple turns </li></ul><ul><li>Direction of current, feeding point </li></ul>
  10. 10. Circular loop antenna 1. Loop antenna <ul><li>Gamma matching: variation of T-matching </li></ul><ul><li>Tuning: capacitor, resonant frequency </li></ul> Gamma matching part Tuning part
  11. 11. Gamma matching 1. Loop antenna <ul><li>Folded dipole antenna </li></ul><ul><li>Capacitor needed </li></ul>
  12. 12. Tuning: capacitor 1. Loop antenna 

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