RFID Arena


Introduction to Retail RFID Technology, part 4 - Readers and antennas

The article series introducing the basics of RFID ends with the fourth part, which discusses readers and antennas.

Author: Toni Heijari

A reader (interrogator) is connected to an antenna that can be either integrated into a device or external. When the antenna is external, there are one or several RF connectors which are used to connect the antenna to the RFID reader. In passive UHF RFID systems, a eader equipped with a suitable antenna generates the necessary power for powering up the tag IC. The energy and message are transferred via electromagnetic waves and they are captured by the tag antenna. The tag uses the backscatter method to deliver its message back to the RFID reader. It reflects a part of the reader's signal back to the reader, but simultaneously modulates its message into the backscatter signal.

about the readers

There are different kinds of RFID readers available on the market depending on the use case and user environment. The readers can be roughly divided into two categories - mobile and fixed readers. Mobile readers are designed for portable use and are easy to carry along while performing inventory for example on the shop floor. There are several types of fixed readers - they can be used at point-of-sale, in RFID gate solutions and for area reading.

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A reader can add different operations into the tag. It can read or write information into different memory banks located in the tag. It can also lock the tag in order to prevent future read / write operations that are performed without a correct password, or it can completely kill the tag. The last option means that the tag cannot be used anymore.

There are a few different standards that are used in UHF RFID. Nowadays, the ISO 18000-6C is the only standard which is used on a wide scale. There are some RFID readers in the market that support other standards as well. These standards define specifically how the communication between the reader and the tag is established and carried out. They also define the used commands, memory allocations and anti-collision algorithms. The last one is needed for communicating in environments where multiple tags are located in the reading area.

The read distance between the reader and the tag is affected by the reader output power, the gain of the reader antenna, the gain of the tag antenna and the sensitivity of both the reader and the tag IC. In UHF RFID, the reading distance can be more than 10 meters.

About the antennas

The antenna transforms the conducted power into radio waves which travels wirelessly in the environment nearby. The radiation pattern of the used antenna defines where the transmission is sent. Usually in UHF RFID, directive antennas are in use. This means that antenna has a clear direction in which it radiates. There are also omni-directional antennas which do not have a specific radiation direction.

There are some other parameters that define the performance of the antenna as well. The gain describes how much the antenna radiates in a specific direction. The polarization of the antenna is also important as the tag antennas are generally linearly polarized. If the reader's antenna is linearly polarized, it must be ensured that the polarization of the tag and the reader are the same (vertical or horizontal). In addition, there are antennas that are either circularly or dual-linearly polarized. Using these kinds of antenna in a reader makes the system more orientation insensitive. Another antenna parameter is efficiency. This indicates the amount of power the antenna radiates in comparison to the power which is fed to the antenna.

To sum up the article series, we have now introduced to you the basics of RFID technology in retail environment. The basics are applicable in other business areas as well.

Read also the previous parts:

Introduction to Retail RFID Technology, part 1

Introduction to Retail RFID Technology, part 2 - Radio technology and radio waves

Introduction to Retail RFID Technology, part 3 - Tags

15 comments on “Introduction to Retail RFID Technology, part 4 - Readers and antennas”

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