Principles of Antennas

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Chapter 5

• Principles of Antennas

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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,

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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.

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Types of Antennas

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

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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,

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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

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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,

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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.

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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,