Antennas: Understanding the Fundamentals

Overview

• Antennas are essential in telecommunications.
• They convert electromagnetic waves to electric signals and vice versa.
• Focus: The underlying science of antennas.

Conversion of Electric Signals to Electromagnetic Waves

• Closed Conductor & Electromagnetic Induction: Produces fluctuating magnetic and electric fields that don't propagate.
• Objective: Separate and propagate electromagnetic waves from the source.

Physics Behind Wave Separation

• Dipole Arrangement: Consists of a positive and a negative charge, creating an electric field.
• Oscillation of Charges:
  • Charges oscillate with maximum velocity at the midpoint and zero velocity at the ends.
  • Oscillating charges experience continuous acceleration and deceleration.
• Electric Field Variation:
  • Wavefront expands and deforms over time due to memory effects in the electric field.
  • The kink generation in the electric field leads to wave separation and propagation.
  • Varying electric field generates a perpendicular varying magnetic field.
  • Wave propagation is sinusoidal, with the wavelength being double the dipole length.

Antenna as a Transmitter

• Construction: Conducting rod with a central bend and time-varying voltage signal.
• Dipole Effect:
  • Voltage displaces electrons, creating positive and negative charges at the wire ends.
  • Positive and negative charges oscillate, producing wave propagation.
• Frequency: Transmitted signal frequency matches applied voltage signal frequency.
• Antenna Length: For optimal transmission, the antenna should be half the wavelength.

Antenna as a Receiver

• Operation: Reversible; applies electric field to the antenna.
• Charge Accumulation:
  • Electric field accumulates electrons at one rod end, inducing dipole effect.
  • Varying electric field causes positive and negative charges to alternate ends.
• Voltage Signal: Produced at the center, frequency matches the incoming electromagnetic wave.
• Antenna Size: Should be half the wavelength for optimal reception.

Practical Antennas

• Dipole Antennas:

  • Previously used for TV reception.
  • Includes dipole, reflector, and director (Yagi-Uda antenna).
  • Signals converted to electrical via coaxial cable to TV.

• Dish TV Antennas:

  • Components: Parabolic reflector and Low-Noise Block Downconverter (LNBF).
  • Parabolic Dish: Focuses signals onto LNBF through feedhorn and waveguide.
  • LNBF Components: Probe induces voltage, PCB processes signal (filtration, conversion, amplification).
  • Double Probes: Detect horizontal and vertical polarized signals.
  • Function: Converts signals to electrical and transmits to TV.

• Cell Phone Antennas (Patch Antennas):

  • Metallic patch on a ground plane with dielectric material.
  • Metallic patch acts as the radiating element.
  • Length should be half the wavelength for effective transmission and reception.
  • Description provided is basic; further research required for detailed understanding.