Notes on Antennas

Introduction to Antennas

• Antennas are essential in telecommunications.
• They convert electromagnetic waves to electric signals and vice versa.

Science Behind Antennas

• Conversion Process:
  • Electromagnetic waves need to be separated from the source to propagate.
  • Closed conductors create fluctuating magnetic/electric fields, but these do not transmit signals.

Understanding Wave Separation

• Dipole Arrangement:

  • Comprises one positive and one negative charge.
  • Produces an electric field.
  • Oscillation leads to continuous acceleration and deceleration of charges, affecting the electric field.

• Electric Field Variation:

  • Wavefront expands and deforms over time due to oscillation of charged particles.
  • Memory effects of the electric field lead to complex field formations.
  • Varying electric fields create varying magnetic fields, leading to wave propagation.

Antenna Design

• An antenna can be constructed by arranging oscillating positive and negative charges.
• Practical Example:
  • Conducting rod with a bend at its center, applying a time-varying voltage creates oscillating charges.
  • This mimics the dipole's behavior, enabling wave propagation.

Antenna as a Transmitter

• The transmitted signal frequency matches the applied voltage signal frequency.
• For effective transmission, antenna length should be half of the wavelength.

Antenna as a Receiver

• When receiving, the antenna converts electromagnetic fields into voltage signals.
• Again, effective reception requires antenna length to be half of the wavelength.

Practical Antenna Examples

• Dipole Antennas:

  • Used in older TV reception systems (e.g., Yagi-Uda antenna).
  • Consists of a dipole, reflector, and director to focus signals.

• Dish TV Antennas:

  • Comprises a parabolic reflector and low noise block down converter (LNBF).
  • Parabolic shape focuses satellite signals onto the LNBF.
  • LNBF includes a feed horn, waveguide, PCB, and probe for signal processing.

• Cell Phone Antennas:

  • Use patch antennas consisting of a metallic patch on a ground plane with dielectric material.
  • Patch length should be half of the wavelength for optimal functionality.

Conclusion

• Antennas play a crucial role in signal transmission and reception in various telecommunications applications.