Antenna of the RFID system can be generally divided into two categories: electronic tag antenna and reader antenna, which can also be subdivided into omnidirectional antenna and directional antenna according to the directivity, and can be divided into linear antenna and planar antenna according to the shape difference. RFID reader antennas need to have the characteristics of wide band and circular polarization. In low and high frequency bands, electronic labels and readers are basically coil antennas, generally using copper wire. However, due to the high frequency used by the high frequency, the number of loops of the antenna will be much less than the low frequency, which makes the production of the high frequency RFID antenna simpler and the price is lower. In the UHF band, more etching processes are used, including copper etching antenna and aluminum etching antenna, and the process is also relatively mature. In the microwave frequency band, the antenna forms are more diversified, including symmetrical oscillator antenna, microstrip antenna, array antenna, broadband antenna and so on
1. Gain coefficient
The gain coefficient is a parameter that comprehensively measures the energy conversion and directional characteristics of an antenna. It is defined as: the product of the directional coefficient and the efficiency of the antenna, which is expressed as:
D is the direction coefficient and the antenna efficiency.
It can be seen that the higher the antenna direction coefficient sum, the higher the gain coefficient.
Physical significance: The gain factor of the antenna describes how much the antenna amplifies the output power in the maximum radiation direction compared to an ideal nondirectional antenna. It can also be popularly understood as the ratio between a directional antenna and an ideal omnidirectional antenna (whose radiation is equal in all directions) to produce a signal of a certain size at a certain point over a certain distance.
For example, if an ideal non-directional point source is used as the transmitting antenna, 100W input power is required, while a directional antenna with a gain of G = 13 dB = 20 is used as the transmitting antenna, the input power is only 100/20 = 5W. In other words, the gain of an antenna, in terms of its radiation effect in the maximum radiation direction, is a multiple of the input power amplification compared with an ideal non-directional point source.
2. Direction of polarization
The polarization characteristic refers to the rule that the direction of the electric field vector in the maximum radiation direction of the antenna changes with time.
The direction of polarization is the direction of the electric field of the antenna. Antenna polarization mode Wired polarization mode Wired polarization (horizontal polarization and vertical polarization) and circular polarization (left polarization and right polarization).
