Many different devices use radio frequency identification (RFID) to communicate information over short distances. RFID units are capable of transmitting on a variety of radio frequencies; however, many countries including the United States mandate that only the ultra high frequency (UHF) range can be used. There are four common types of UHF RFID antenna designs. All of them can be used for UHF data transfer, but each antenna design has a specific advantage.
RFID systems consist of a tag or label, and an antenna for reading data. The tags are able to transmit embedded information when they are close enough to the antenna. To ensure an effective data transfer, antennas and tags are specifically designed to operate on one specific radio frequency.
A pass through rectangle UHF RFID antenna is designed to cover a relatively large area. In this design, the antenna wires form a broad circuit with square corners. In order for RFID tags to be detected, they must pass through the center opening of the rectangle. These types of UHF RFID antenna can be used in doorways where people naturally move through the middle of an opening. A sensor for detecting stolen merchandise when a person exits a building is one common application of this antenna design.
UHF RFID antennas can also be arranged in a circular loop design. This type of setup uses two circular loops of antenna wire, which are placed a moderate distance apart. As a tag moves past both antennas, the time difference between the two wires can be recorded. Comparing the order and delay of data from the twin antennas allows the RFID reader to calculate the direction and speed that an object is traveling. This information can be useful in an factor or other installation with different moving parts.
A pass over loop is a type of UHF RFID antenna that is optimized for scanning tags placed on a flat, horizontal surface. Like a pass through rectangle design, a pass over loop antenna uses only one wire that forms a circuit. This design does not require the tag to move through the center opening. Instead, RFID data can be read when the antenna loop comes into very close proximity with a tag. This design is optimized for short range scanning tasks, such as indexing tagged books that are spread out on a table.
The fourth type of UHF RFID antenna is the pass by loop. This design is essentially the same as a pass over loop, except the antenna wire is pivoted into a vertical orientation. The pass by loop antenna is used for collecting data from an RFID tag that is deliberately swiped past the wire. A security card reader is one of the most common applications for this antenna layout.