What coaxial cable antenna near field
In the previous article, Xiaotian talked about the far field of the coaxial cable antenna. This time, Xiaotian will take you to understand the far field of the coaxial cable antenna.
The radio wave of a coaxial cable should be called an electromagnetic wave or simply an EM wave because the radio wave contains an electric field and a magnetic field. The signal from the transmitter, via the antenna, generates an electromagnetic field, and the antenna is the signal to the free space converter and interface.
Therefore, the change in the characteristics of the electromagnetic field depends on the distance from the antenna, and there seems to be no formal definition of the near field - it depends on the application itself and the antenna. Generally, the near field refers to the distance from the beginning of the antenna to one wavelength (λ). The wavelength unit is meters and the formula is as follows:
λ = 300/fMHz
Therefore, the distance calculation method from the antenna to the near field is as follows:
λ/2π = 0.159λ
The near field is usually divided into two regions, a reaction zone and a radiation zone. In the reaction zone, the electric and magnetic fields are the strongest and can be measured separately. Depending on the type of antenna, a certain field will become dominant. For example, the loop antenna is mainly a magnetic field, and the loop antenna is like the primary of a transformer because it generates a large magnetic field.
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