Radio frequency: RF for short. Radio frequency is radio frequency current, which is the abbreviation of high frequency AC electromagnetic wave. Alternating current that changes less than 1000 times per second is called low-frequency current, and that that changes more than 10000 times is called high-frequency current, and radio frequency is such high-frequency current.

At present, the most widely used automatic identification technology can be roughly divided into two aspects: optical technology and radio technology. Among them, the products widely used in optical technology are: bar codes and cameras. These two products have been widely used in people's daily life and are widely known. For example, bar codes are used for commodity management, and cameras are used to capture illegal vehicles.

Microwave: The frequency of microwave is extremely high and the wavelength is very short. Its propagation characteristics in air are similar to those of light waves, that is, it goes straight ahead and is reflected or blocked when encountering obstacles. Therefore, the main mode of microwave communication is line-of-sight communication, which requires relay after exceeding the line-of-sight distance. For microwave communication, electromagnetic wave-microwave with wavelength between 0. 1mm- 1m is used. Microwave communication does not need solid medium, and it can be used when there is no obstacle within the linear distance between two points.

Microwave communication has large capacity and good quality, and can be transmitted to far places. Therefore, it is an important means of communication in the national communication network and is generally suitable for all kinds of special communication networks.

L, S, C and X bands are widely used in microwave communication in China, and the application of K band is still under development.