Antenna Theory: aerial basics

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Antennas are a key element of any radio system. An antenna is required to radiate and receive the signals and therefore their performance is key to the operation of the overall radio system.

If the antenna performance is poor, then it will limit the performance of the overall system. As such, maximising the performance of the antenna is very important. An understanding of basic antenna theory will help the maximum be gained from any aerial system.

Key antenna theory topics

There are several basic topics that are common to all antenna types and which form part of the basic antenna theory.

  • Polarisation:   Radio antennas are sensitive to polarisation. In just the same way that electromagnetic waves can be polarised, so to are antennas. It will be seen that some antennas have their elements in a vertical fashion and others are horizontal. This is to accommodate vertical and horizontally polarised electromagnetic waves.
  • Resonance & bandwidth:   Resonance and bandwidth are key issues for antenna theory. Most antennas operate in a resonant fashion and in this way they are able to perform to their best. Associated with this is the bandwidth over which they are able to operate.
  • Gain & directivity:   Antennas do not radiate equally in all directions – only an isotropic source radiates equally in all directions and this is a theoretical entity only . In some directions practical antennas exhibit gain where the available power is focussed in a particular direction, and they have a directional pattern. Antenna theory for directivity and gain is important in many areas.
  • Feed impedance & matching:   The input connection to an antenna presents an impedance to the feeder to which it is connected. For optimum power transfer source and load should be matched. Accordingly antenna theory associated with the feed impedance is important for the optimum operation of the antenna.

Antenna theory is an enormous topic. Even the antenna basics form a large, but nevertheless a very interesting topic.

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