The main parameters of the RFID antenna you have to look at

As we all know, RFID Antenna is an indispensable part of RFID system. In a wireless communication system, it is necessary to convert the guided wave energy from the transmitter into radio waves, or convert radio waves into guided wave energy, and the device used to radiate and receive radio waves is called an antenna.

The main parameters of the RFID antenna

1. Gain coefficient

The gain coefficient is a parameter that comprehensively measures the energy conversion and directional characteristics of the antenna. It is defined as the product of the directional coefficient and the antenna efficiency. It can be seen that the higher the antenna direction coefficient sum is, the higher the gain coefficient will be.

Physical meaning: In the case of the same input power, the ratio of a directional antenna to an ideal omnidirectional antenna (its radiation is equal in all directions) generates a certain size of signal at a certain point at a certain distance. It describes the degree to which an antenna concentrates the input power and radiates it. .

2. Beam width

When the operating frequency changes, the relevant electrical parameters of the antenna should not exceed the specified range. This frequency range is called the beam width, or the bandwidth of the antenna for short.

3. Direction coefficient

       At a certain distance from the antenna, the ratio of the radiation power flow density of the antenna in the maximum radiation direction to the radiation power flow density of an ideal non-directional antenna with the same radiation power at the same distance. This is the most important indicator of directivity, which can accurately compare the directivity of different antennas, and represents the electrical parameters of antenna beam energy.

4. Impedance

The antenna can be regarded as a resonant circuit. A resonant tank of course has its impedance. Our requirement for impedance is matching: the circuit connected to the antenna must have the same impedance as the antenna. The feeder is connected to the antenna, and the impedance of the feeder is determined, so we hope that the impedance of the antenna is the same as the feeder. The RFID UHF antenna system uses a 50Ω impedance feeder.

5. Polarization method

The polarization of the antenna refers to the direction of the electric field strength formed when the antenna radiates. In general, it refers specifically to the spatial orientation of the electric field of the antenna in the direction of maximum radiation. The polarization of the antenna is mainly divided into linear polarization and circular polarization, so what are the differences?

Linear polarization:

When the polarization direction of the receiving antenna is consistent with the linear polarization direction (electric field direction), the induced signal is the largest; as the polarization direction of the receiving antenna deviates more and more from the linear polarization direction, the induced signal The smaller; when the polarization direction of the receiving antenna is orthogonal to the linear polarization direction (magnetic field direction), the induced signal is zero.

Circular polarization:

Regardless of the polarization direction of the receiving antenna, the induced signal is the same, and there will be no difference. Therefore, the use of circular polarization reduces the sensitivity of the system to the orientation of the antenna.

Because only when the polarization direction of the receiving antenna is consistent with the polarization direction of the received electromagnetic wave can the maximum signal be induced. Therefore, the linear polarization method has higher requirements on the direction of the antenna. However, the circular polarization method is adopted in most occasions because of its functions.

6. Voltage standing wave ratio

VSWR reflects the matching condition of the antenna-feed system. It measures the antenna performance by the ratio of the energy emitted and reflected back when the antenna is used as a transmitting antenna. The VSWR is determined by the impedance of the antenna feed system. The impedance of the antenna and the impedance of the feeder are consistent with the impedance of the receiver, and the standing wave ratio is small. For an antenna-feeder system with a high VSWR, the signal loss in the feeder is very large.