Chapter 5 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,

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.

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

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

Semi Directional Antenna’s 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

Highly Directional Antenna’s 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,

Passive vs. Active Gain Passive Gain The total amount of energy emitted by the antenna doesn’t 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.

Let’s 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”,