What are the different effects of two electromagnetic wave f

　　Everyone knows that the magnetic field is far and near. We also know that the signals are divided into electromagnetic waves. Today, the small edition tells you a more profound question. That is, what different effects do the two electromagnetic wave fields have on the antenna? Let's go to the manufacturer of electronic antenna to do an experiment together.

　　The antenna is an energy conversion device. The transmitting antenna converts the guided traveling wave into the space radiated wave, while the receiving antenna converts the space radiated wave into the guided traveling wave. Therefore, a transmitting antenna can be regarded as the source of radiating electromagnetic waves, and the distribution of field intensity around it is generally a function of the distance away from the antenna and the angular coordinates. Generally, the field area around the antenna is divided into induction field area, radiation near field area and radiation far field area according to the distance from the antenna.

　　(1) Reactance near field

　　The induction field is the area close to the antenna. In this field, the electromagnetic wave is not radiated, and the electric field energy and magnetic field energy are stored alternately in the space near the antenna. The outer boundary condition of the induction field of an electrically small dipole antenna is l/2p. Here, L is the working wavelength.

　　(2) Radiation near field

　　The relative angular distribution of electric field in the radiation near field (Fresnel zone) is related to the distance away from the antenna, that is, the pattern is different at different distances. This is because:

　　*The relative phase relation of the field established by the radiation sources of the antenna varies with the distance.

　　*The relative amplitudes of these fields vary with distance. The antenna pattern at the inner boundary of the radiation near-field (i.e. the outer boundary of the induction field) is a fluctuating envelope of the main lobe and the side lobe.

　　*With the increase of the distance from the antenna until near the far field radiation area, the main lobe and the side lobe of the antenna pattern are obviously formed, but the zero level and the side lobe average are higher. The outer boundary of the radiation near-field region is defined as:

　　r=2D2/λ(m) （1.3.1）In the formula, R is the distance from the observation point to the antenna.

　　(3) Far-field radiation

　　Outside the radiation near-field region is the radiation far-field region (Fraunhofer region). The region is characterized by:

　　*The relative angular distribution of the field is independent of the distance from the antenna.

　　*The size of the field is inversely proportional to the distance from the antenna.

　　*The main lobe, the side lobe and the zero point of the pattern have all been formed.

　　The far-field radiation region is an important field for antenna testing, in which all parameters of antenna radiation characteristics should be measured. In practical measurements, the distance between the near and far fields shown in the accepted formula must be observed.

　　It's hard for us laymen to understand, so if we don't know anything, we must come to the manufacturer of electronic antenna to consult and confirm it in time.