RFID Antenna Selection Guide: Gain and Polarization Explained
Choosing the right RFID antenna is not an easy task. When you see
parameters like "9dBi" and "12dBi", it's easy to get confused about what these
numbers mean in real-world applications. To complicate matters, you'll also
encounter antennas described as "linear" or "circular" polarized.
With 15 years of experience in RFID technology, I can say for sure: antenna
gain (measured in dBi) and polarization are both critical. Here's how to explain
what these terms mean, the difference between 9dBi and 12dBi antennas, and how
to choose the best antenna for your needs.
What does "dBi" mean?
First, a little jargon. "dBi" is decibels relative to an isotropic
radiator, which in layman's terms measures an antenna's ability to focus energy
in a specific direction, compared to an ideal, evenly radiating antenna.
High dBi (like 12dBi): Focusing energy in a narrower beam means longer read
distances but a smaller coverage area.
Low dBi (e.g. 9dBi): Energy is spread over a wider area, providing better
coverage, but with a shorter read distance.
A flashlight analogy can be used: a high-gain antenna is like a focused
beam that shines farther, while a low-gain antenna is like a lantern,
illuminating a wider area but at a shorter distance.
What is Polarization? (Linear vs. Circular)
Polarization describes the orientation of the radio waves as they leave the
antenna, and there are two main types:
Linear Polarization
Linearly polarized electromagnetic waves propagate in a single plane
(vertical or horizontal). Linear antennas are best when it is known that the
orientation of the RFID tag will always be the same as the antenna
orientation.
Pros: Longer read distance (about 10-20% more than circular polarization),
less energy loss.
Cons: Read reliability decreases if the tag is tilted or misaligned.
Circular Polarization
Circularly polarized electromagnetic waves rotate in a circle as they
propagate, covering all possible orientations of the tag.
Pros: More adaptable, able to read regardless of how the tag is tilted or
positioned.
Disadvantages: Slightly shorter read distance than linear polarization, but
more versatile.
In short:
When tag orientation is controllable and consistent, choose a linearly
polarized antenna.
When tag orientation is random or unknown, choose a circularly polarized
antenna.
Home >
+86 186 8871 1070
