Antennas

Section 1: Introduction to Antennas

  • An antenna is a device used to transmit and receive electromagnetic waves.
  • Antennas form the essential link between free-space and electrical current in wireless communication systems.
  • The key characteristics of an antenna include directionality, gain, and polarisation.
  • Antennas can operate over a range of frequencies, from kilohertz (kHz) to gigahertz (GHz).

Section 2: Types of Antennas

  • There are myriad types of antennas, including dipole antennas, monopole antennas, loop antennas, and dish antennas, among others.
  • A dipole antenna is the simplest and most widely used type of antenna, typically resonant at half a wavelength.
  • A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane.
  • Loop antennas are particularly used for their directional properties, and large dish antennas are used for their high gain in satellite and radar systems.

Section 3: Antenna Parameters

  • Key parameters of antennas include impedance, radiation pattern, polarization, and gain.
  • Impedance matching is a fundamental aspect of antenna design, ensuring the impedance of the antenna and the transmission line are the same to minimize signal reflection.
  • The radiation pattern characterises the directional dependance of the field strength transmitted or received by the antenna.
  • Polarization refers to the orientation of the electric field of the electromagnetic wave transmitted by the antenna.
  • Gain is a measure of an antenna’s directivity; a higher gain indicates the antenna can transmit or receive more power in specific directions.

Section 4: Antenna Applications

  • Antennas find their usage in a variety of applications, from simple broadcast radios to complex systems within airplanes and satellites.
  • In telecommunication systems, antennas are used in transmitting stations for broadcasting radio waves and in receiving stations to capture those waves.
  • Directional antennas are used in systems like radar, in which the energy should be concentrated in one direction.
  • Radio telescope antennas are used for capturing radio signals from space in astronomy research.
  • Antennas used for GPS applications are generally small and lightweight, providing reliable navigation data.