An antenna is a basic component of any electronic system which depends on free space as a propagation medium.
An antenna is a device which provides a means for radiating or receiving radio waves. It is a transducer between a guided electromagnetic wave and an electromagnetic wave propagating in free space.
In a communications link, the transmitter is connected through a cable or waveguide to one antenna, the signal is radiated to another antenna, and then passes through another cable or waveguide to the receiver.
There are several different types of antennas in three broad categories:
- Omni-directional — antennas propagate in all directions.
- Directional — antennas have a narrow “beam” that allows highly directional propagation; familiar types are the parabolic and Yagi. Each has unique characteristics and applications.
- Semi-directional — antennas propagate in a constricted fashion, defined by a specific angle.
Dipole antennas are the most common type of antenna used and are omni-directional, propagating radio frequency (RF) energy 360 degrees in the horizontal plane. These devices are constructed to be resonant at a half or quarter wavelength of the frequency being applied.
This antenna can be as simple as two pieces of wire cut to the proper length or can be encapsulated. This configuration is commonly referred to as a “rubber ducky” antenna. The dipole is used in many enterprise and small office and home office (SOHO) Wi-Fi deployments.
It is essential to understand the three most important specifications of an antenna: frequency, beam width and gain, in order to choose an antenna most perfectly suitable for your wireless needs.
Frequency refers to the data transmission between any two points by electromagnetic waves as they carry a certain amount of kinetic energy therewith. This associated energy of a wave is directly proportional to the wave’s frequency.
Beam width is a measurement of the area over which the antenna receives a signal. In most cases, it is measured to the “half-power points,” which is the number of degrees between the points where the gain is 3 dB less than the gain for the antenna’s strongest direction.
Gain measures an antenna’s ability to amplify incoming signals. In other words, the gain value directly determines the antenna’s receiving strength.
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