Even though RFID antennas are not the brains of an RFID system, they are still complex devices that can hinder or benefit an RFID system depending on the application and chosen antenna. For instance, choosing the wrong antenna for a certain application could result in inches of read range instead of feet. Besides the basic guidelines for choosing an antenna like gain and polarization, other factors exist that could take a system’s read range and results to the next level. Beamwidth and directionality are two core principles to grasp in order to make a more informed purchasing decision.
Beamwidth
Beamwidth is defined as “the angle between two points on the same plane where the radiation falls to ‘half power’, or 3 dB below the point of maximum radiation.”¹. It can also be thought of as the peak effective radiated power of the main lobe. Most usually think of beamwidth as the horizontal angle on a radiation pattern, but there are two beamwidths – azimuth (horizontal) and elevation (vertical).
Azimuth vs. Elevation
If the antenna is on a 3D plane, like below, you will be able to accurately see the azimuth and elevation beamwidths. Understanding the azimuth and elevation beamwidths of an RFID antenna enables a person to choose the best antenna for their application. In some applications, a very wide azimuth or elevation beamwidth is needed in order to read all the tagged items lined up in, for example, a small room. In other applications, like a conveyor belt, a thinner, acute beam is better fitted. Some antenna data sheets actually show the 3D model of the azimuth and elevation beamwidths, while other manufacturers’ data sheets show 2D models. The 2D models are more basic, but are still able to clearly show the beamwidth in both planes.
Directivity
The directivity of antenna is defined as “its ability to focus in a particular direction to transmit or receive energy”¹. The way that an antenna directs its energy is a huge factor in both choosing an antenna and setting up an application. If an antenna is set up in an application and the type and radiation pattern is not known, the tagged items might not be read or be affected by absorption, diffraction, reflection, and refraction. Antennas can be grouped in two different sets based on directivity – isotropic or anisotropic, or omni-directional or directional.
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