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Principles of Antennas

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Chapter 5 Principles of Antennas Principles of Antennas Antennas convert electrical energy into RF waves in the case of a transmitting antenna, RF waves into ... – PowerPoint PPT presentation

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Title: Principles of Antennas


1
Chapter 5
  • Principles of Antennas

2
Principles of Antennas
  • Antennas convert electrical energy into RF waves
    in the case of a transmitting antenna, RF waves
    into electrical energy in the case of a receiving
    antenna,
  • The physical dimensions of an antenna, such as
    its length, are directly related to the frequency
    at which the antenna can propagate waves, or
    receive propagated waves,
  • The physical structure of an antenna is directly
    related to the shape of the area in which it
    concentrates most of its radiated RF energy,

3
Types of Antennas
  • An RF antenna is a device used to convert high
    frequency signals (RF) on a transmission line (a
    cable) into propagated waves in the air,
  • The RF fields emitted from antennas are called
    beams, or lobes.

4
Types of Antennas
  • There are three generic types of RF antennas,
  • Omni directional,
  • Semi-directional,
  • Highly-directional,

5
Omni directional Antennas
  • An omni directional antenna radiates energy
    equally in all directions around the antennas
    vertical axis.
  • The most common type is a dipole antenna,

6
Semi Directional Antennas
  • Typically focus coverage in a horizontal arc of
    180 degrees, or less, as opposed to a 360 arc for
    an omni directional antenna,
  • Examples
  • Yagi,
  • Patch,
  • Panel

7
Highly Directional Antennas
  • Highly directional antennas emit the most narrow
    signal beams of any antenna type and have the
    greatest gain of all three groups of antennas,
  • Examples
  • Parabolic Dish
  • Grid
  • Most used for Line of Sight (LOS) applications,

8
Passive vs. Active Gain
  • Passive Gain
  • The total amount of energy emitted by the antenna
    doesnt increase, only the distribution of the
    energy around the antenna can change.
  • Active Gain
  • Active gain is the type of gain achieved through
    the use of an amplifier. The amount of energy
    increases without changing the shape of the
    coverage area.

9
Lets Design an antenna
  • Log into your computer,
  • Start up the 4NEC2x software,
  • Look in the f drive for the NEC software folder,
    Project files sub-folder,
  • Open up the file named dipole.nec,
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