Classification Of RFID Antennas

RFID antenna is an important component of RFID system, which is an interface device between circuit and space. It is a window for converting guided wave and free space wave energy. There are many types of RFID antennas, which can be used in different frequencies, purposes, occasions, requirements, and other situations.

Classification of RFID antennas
RFID antennas can generally be divided into RFID tag antennas and RFID reader/writer antennas, which can be further divided into omnidirectional antennas and directional antennas based on their directionality; According to the differences in appearance, it can also be divided into linear antennas and planar antennas, etc; According to the design process of antennas, there are three basic forms: coil type, microstrip patch type, and dipole type.

Low frequency and high frequency RFID basically use coil antennas, usually using copper wire. The coil antenna coils the metal wire into a plane or wraps it around the magnetic core. Strictly speaking, this type of coil cannot be considered an antenna, but is actually a coil mutual inductance effect and has a simple process. The area of the coil is related to the recognition distance. Due to the high frequency used at high frequencies, the number of circles the antenna is wound much less than at low frequencies, which makes the production of high-frequency RFID antennas simpler and cheaper.

The antennas used in ultra-high frequency RFID are real antennas, and there are many etching processes used, including copper etching antennas and aluminum etching antennas. The processes are also relatively mature, and antennas are required for electronic tags and readers in ultra-high frequency RFID. The antenna in electronic tags needs to be matched with a complex impedance, which is determined by the tag chip, and the complex impedance of each chip is different. Therefore, the antenna line type cannot be universal, and a new chip requires a redesigned antenna. There are various types of ultra-high frequency tag antennas, and the commonly used ones are dipole antennas. Dipole antennas are composed of two straight wires of the same thickness and length arranged in a straight line, and the signal is fed from the middle two endpoints. The length of the antenna determines the frequency range. Dipole antennas have the advantages of good radiation energy, simple structure, and high efficiency; The ultra-high frequency reader antenna is mainly composed of plate shaped antennas, in addition to rod shaped antennas and near-field antennas. In ultra-high frequency RFID, the antenna is one of the important determining factors for reading distance, and the radiation range and direction are completely determined by the antenna.

Microstrip patch antennas have the characteristics of low profile, light weight, simple processing, easy conformability with objects, and diverse electrical performance. They are composed of radiation patch conductors attached to dielectric substrates with metal substrates. Based on the radiation characteristics of the antenna, patch conductors can be designed in various shapes. The microstrip patch antenna consists of a circuit board with a rectangle at the end, and the length and width of the rectangle determine the frequency range.

Technical parameters of RFID antenna
The main technical parameters of the RFID reader antenna include frequency band, gain, standing wave, front to back ratio, beam width, and polarization direction; The technical parameters of RFID tag antenna mainly include frequency band, gain, polarization direction, standing wave, directional pattern, etc.

1. Gain
The gain coefficient is a parameter that comprehensively measures the energy conversion and directional characteristics of an antenna. It is the product of the directional coefficient and antenna efficiency. The higher the sum of antenna directional coefficients, the higher the gain coefficient.

2. Polarization direction
Polarization characteristics refer to the temporal variation of the direction of the electric field vector in the radiation direction of an antenna. The polarization direction is the direction of the antenna's electric field, and the polarization methods of the antenna include linear polarization (horizontal polarization and vertical polarization) and circular polarization (left-handed polarization and right-handed polarization).

Generally speaking, low-frequency and high-frequency close range application systems with a recognition distance of less than 1m generally use coil type antennas with simple technology and low cost; Dipole and microstrip patch antennas are used in ultra-high frequency long-distance application systems above 1m.