Although RFID systems can vary significantly in terms of device types and complexity, they all share four core components: a reader, antenna, tag, and connecting cables. In the simplest systems, this might include only a handheld RFID reader (with an integrated antenna) and RFID tags. In contrast, more complex systems may incorporate multi-channel readers, GPIO (General Purpose Input/Output) modules, additional functional devices (such as status indicator light arrays), multiple antennas, connecting cables, RFID tags, and comprehensive supporting software.
The RFID antenna plays an indispensable role in an RFID system. Its purpose is to convert the signal from the RFID reader into radio frequency (RF) waves, ensuring that the RFID tag can effectively receive the signal. Without an appropriate RFID antenna—whether integrated or standalone—the RFID reader would be unable to successfully transmit or receive signals to and from the RFID tag.
RFID antennas differ from RFID readers. Unlike readers, RFID antennas are passive devices that draw their operating energy from the reader. When the reader transmits energy to the antenna, the antenna generates an RF field and sends RF signals to nearby tags. The efficiency of an antenna in generating waves in a specific direction is referred to as antenna gain. In simple terms, the higher the gain, the stronger the RF field and the broader the coverage area of the antenna.
RFID antennas emit RF waves either horizontally or vertically, which is defined as the antenna's polarization. If the RF field lies on a horizontal plane, it is described as horizontally linear polarization. Similarly, if the RF field lies on a vertical plane, it is referred to as vertically linear polarization.
The working principle of an RFID antenna is based on wireless communication technology, enabling the wireless reading and writing of information stored in tags by transmitting and receiving electromagnetic signals. The process can be explained in the following aspects:
1. Signal Transmission and Reception
The RFID antenna is responsible for transmitting and receiving radio frequency (RF) carrier signals. Once the operating frequency and bandwidth are defined, the antenna emits RF carrier waves generated by the RF processing module and receives the RF signals emitted or reflected by the tags. These RF signals form the foundation of wireless identification and data exchange within an RFID system.
2. Electromagnetic Energy Conversion
Passive RFID tags do not have internal power sources like batteries, so they rely on the electromagnetic waves sent by the reader to obtain the energy needed to activate their circuits. When the antenna receives the electromagnetic signals transmitted by the reader, it uses an inductive coil and resonant circuit to convert the electromagnetic waves into alternating current, providing power to the circuits within the tag.
3. Information Transmission and Processing
Once the RFID tag obtains sufficient energy and is activated, its internal circuits read or write information stored in the tag’s chip. This information is transmitted back to the reader via RF signals through the tag's antenna. The reader’s receiving antenna captures the signals from the tag, and the signal processing module demodulates and decodes the information, sending the useful data to the backend system for further processing.
4. Electromagnetic Field Functionality
The RFID antenna creates an electromagnetic field between the reader and the tag, which is essential for enabling wireless identification and data exchange. When an RFID tag enters the reader's active working zone, the tag’s antenna induces a current from the electromagnetic field, generating the necessary power for its circuits. At the same time, the tag antenna uses the electromagnetic field to send the stored information in the tag back to the reader as RF signals.
This combination of electromagnetic field generation, energy conversion, and signal processing ensures effective communication and functionality within an RFID system.
The polarization method of the RFID antenna determines the propagation direction of the RF signal. There are mainly the following two kinds:
1. Linearly polarized antenna
RF signals emitted by linearly polarized antennas propagate along a fixed direction, which can be a horizontal or vertical polarized wave. This type of antenna is characterized by concentrated signals and a longer reading range, but it needs to be aligned with the polarization direction of the RFID tag to obtain the best reading results.
Applicable scenarios: suitable for RFID tag direction fixed scenarios, such as conveyor belt on the items read.
2. Circularly polarized antenna
Circularly polarized antennas rotate the RF signal between horizontal and vertical directions as it propagates. Although its signal range is slightly smaller than that of a linearly polarized antenna, it is able to read RFID tags in a variety of directions, providing more flexibility.
Scenarios: Suitable for scenarios where tag orientation is not fixed, such as retail, warehousing or inventory management.
