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SUMMARY

  1. An antenna is a logical arrangement of several conductors. It is a transducer. It is also commonly termed an aerial.

  2. The transmitting antenna transmits electromagnetic field waves.

  3. The receiving antenna picks up this electromagnetic field (RF) signal.

  4. An antenna converts electrical currents in the RF signal at the transmission side and then converts back this RF signal into an electrical current at the reception side.

  5. Antenna designs are reciprocal in the sense that all transmitter antenna parameters are also applicable to the receiving antenna (reciprocity theorem).

  6. Antenna tuning refers to charging the electrical resonance in an antenna, which is done by adjusting the length of the antenna.

  7. Antenna shields are used for noise rejection.

  8. The transmitting antenna should have a high power rating.

  9. The receiving antenna should have good noise rejection properties.

  10. Important antenna parameters are resonant frequency, impedance, gain, aperture (radiation pattern), polarization, bandwidth and efficiency.

  11. Antennas are made resonant on harmonic frequencies by having their lengths a fraction of the desired wavelength.

  12. The electrical length of an antenna is the ratio of the physical length of the wire to the velocity factor.

  13. The standing wave ratio (SWR) is the ratio of maximum to minimum measurable power of the wave.

  14. Gain of an antenna is the ratio of radiation intensity power per unit surface in a given direction at an arbitrary distance to radiation intensity of a hypothetical isotropic antenna at the same distance.

  15. Aperture or radiation pattern of an antenna is a 3-D graph.

  16. In an antenna, polarization is the orientation of an electric field (E-plane) due to the radio wave with respect to the Earth's surface.

  17. Polarization can be linear or circular.

  18. On the basis of the direction of propagation, elliptical polarization can be right handed or left handed.

  19. The bandwidth of an antenna is the range of frequencies over which it is most effective.

  20. The efficiency of an antenna is defined as the ratio of radiation resistance to total resistance.

  21. Alternatively, antenna efficiency is also defined as the ratio of actually radiated power to the amount of power put into antenna terminals.

  22. An antenna array is a combination of several antenna elements. It can be of broadside or end fire types.

  23. Retarded potentials are delayed potentials that get established because of time-varying field.

  24. A short dipole antenna is a simple antenna, which is fed at the centre for transmitting and receiving RF signals. These antennas are used in TV, FM bands, etc.

  25. Radiation resistance is given as



  

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