How does a UHF RFID System Work?

The RFID reader emits radio waves of specific frequencies through RFID antennas. The waves "give energy" to the tags so that they can communicate by emitting a unique ID. They do not need batteries and can be used for many years. The reader processes the data so that we can integrate them into our application and give them meaning. The typical reading range is 0-12 meters. Gen2 UHF RFID systems consist of: readers, antennas, printers, and RFID tags or labels. In this article I will define with a brief explanation each of the main elements when implementing an RFID project.


RFID Antennas are responsible for emitting and receiving waves that allow us to detect RFID chips. When an RFID chip crosses the antenna field, it is activated and emits a signal. The antennas create different wave fields and cover different distances.

Antenna Type: Circular polarization antennas work best in environments where the orientation of the tag varies. Linear polarization antennas are used when the orientation of the tags is known and controlled and is always the same. NF (Near Field) antennas are used to read RFID tags within a few centimeters.

Overcast angle and gain: Using antennas with gains of between 8.5-10 dbi or more, will allow us to emit more power and obtain a higher reading ratio. The angle of opening depends on the area to be covered, for example: 70 °, 100 °, etc. The more overture the antennas have, the less detection distance.

Number of Antennas: Standard high-performance readers have 2 ports, 4 ports or 8 ports. The number of antennas is usually chosen according to the reading space we want to detect or the density of tags to read. Typically used is 2 or 4 port fixed readers. Some brands have multiplexers that allow us to connect up to 32 antennas in the same reader.


There are multiple types of readers; Fixed RFID, portable rfid readers, rfid readers for Smartphone and USB readers. To read a high density of tags or requirements of 100% accuracy in detection, the best fixed RFID readers are: Impinj R420, ThingMagic M6e, Zebra FX9500. And if we need to use portable readers, we recommend the Zebra MC9190, Impinj AB700 Zebra RFD8500. To choose the right reader, we have to take into account several factors:

Reading area: Fixed readers serve mainly to cover a specific area: one point by a doorway, a machine, on a conveyor belt, in a crate, etc. Mobile readers allow us to read while we move and to perform inventories or search for RFID tags that we do not see.

Ratio of reading: the emission power and reading capacity requirements are determined by the number of tags to detect in a specific time. The most complex applications are those where there is a high density of tags, liquids or metal products. The maximum reading power is marked by the regulation allowed in each country or zone according to the type of frequency (ETSI, FCC).

The type of rfid reader: many times the question is whether to use a fixed reader or a portable reader. This factor depends on the application. For example, if we are in a store or warehouse where we need to make inventories and movements, it is convenient to use a portable terminal. If the reading area is fixed, it is convenient to install a reader that covers the area and leave the task automated. For example to detect pallets or products in shipping areas.

USB Readers: These readers give excellent results when we need to record or read very few tags at different points during the manufacturing processes or for validation of documents in offices. Two clear examples are the Nordic Stix and the ThingMagic USB Reader.


The essential factors are: size, orientation, reading angle, area the are located and the type of chip.

Size: the size of the chip is a very important factor, for the simple reason that the more antenna the RFID tag, has the better the sensitivity and the detection. Whether the response of the tag is always the same or very similar every time it is detected, we are able to then develop reliable and robust applications. The antennas are usually made of aluminum or copper.

Orientation and reading angle: If we have circular antennas we do not have to worry about much about orientation. The orientation of the tag is worrisome when we try to detect them with linear antennas. In this case, we must test if the best position of the tag is vertical or horizontal, as is the case when using the ShortDipole tag. There are omni directional antennas with two dipoles, such as FROG 3D and WEB, that allow us to detect the tags regardless of their orientation. The reading range of these is usually lower by the composition of the antenna.

Integrate Circuit (IC): These are the internal chips of the RFID tag. The most common are the Impinj Monza, NXP, and Higgs. There are IC's with more or less memory, from 96 bits to 512 bits. They have additional memories, EAS alarm system, ability to lock with passwords, etc. There are also IC's that combine both RFID / NFC technologies on the same chip. When more memory is required we can put it in an external database and associate an ID that identifies the chip.

Location area: it is very important to take into account where the applied tag will go so that the rfid solution is successful and meets the necessary reading ranges. Keep in mind that metal bounces the RF waves and that water absorbs them. There are solutions for metal labels that allow us to place the tags on the metal and detect them correctly. The material and adhesive to be used are determined by environmental factors such as indoor or outdoor, high temperatures, as is the case in pharmaceuticals tracking or food tracking as well as other special applications.

Price tag RFID: If the application requires a large volume of tags, this will surely be the most important factor to determine pricing and measure return on investment.



Many times we wonder how we can encode the information inside the tags. With rfid printers such as Zebra printers ZT410 0 R110xi, we can encode the chip and print any bar code or number. We can also encode tags with USB readers, fixed readers or portable readers. But where do we encode the information? Usually when reading the tags, it is the EPC or TID that is read. TIDs are not modifiable and are composed of a unique number that comes from the factory. The EPC space of the tag is what is recorded, modified and with which we normally interact. The tags have an internal memory (User memory) where we can save additional information.


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