This is how the magic electronic antenna works.

　　Xiaobian is a student of intelligent control. He is particularly interested in this aspect. In the last issue, many small partners contributed papers. They asked to see how the electronic antenna manufacturer works.

　　When high frequency current is applied to a conductor, electric and magnetic fields will be generated in the surrounding space. According to the spatial distribution of electromagnetic field, it can be divided into near zone, middle zone and far zone. Let R be the distance between a point in space and a conductor. The region in time is called the near region. The electromagnetic field in the region is closely related to the current and voltage in the conductor.

　　In the far zone, the electromagnetic field can travel from the conductor to the space, and its change will lag behind the current and voltage on the conductor for a period of time. At this time, the electromagnetic wave propagating out of the region is no longer directly related to the current and voltage on the conductor. The electromagnetic field in this region is called radiation field.

　　It must be pointed out that the radiation is very weak when the length L of the conductor is far less than the wavelength lambda, and when the length L of the conductor is increased to be comparable to the wavelength, the current on the conductor will be greatly increased, thus strong radiation can be formed.

　　The transmitting antenna makes full use of the nature of the radiation field to make the transmitted signal radiate to space after passing through the transmitting antenna. How to make a conductor an effective radiator conduction system?Here we first analyse the situation on the transmission line. In order to make the transmission line of parallel double-line have only energy transmission and noradiation, we must ensure the symmetry of the structure of the two lines, and the magnitude and direction of the corresponding point current on the line.On the contrary, the distance between the two lines is less than pi. In order to radiate the electromagnetic field effectively, it is necessary to destroy the symmetry of transmission lines. For example, by separating two conductors at a certain angle or removing one of them, the symmetry of conductors can be destroyed and radiation can be produced.

　　When the conductor at the open circuit transmission or distance from the terminal pi/4 is separated in a straight line, the current on the terminal conductor is not inverted but in the same phase, so that the radiation field of the conductor at the space point is superposed in the same phase to form an effective radiation system.This is the simplest and most basic element antenna, called half-wave symmetric dipole antenna, whose characteristic impedance is 75_. When the electromagnetic wave radiates from the transmitting antenna, it propagates in all directions. If a pair of symmetrical oscillators are placed in the direction of the electromagnetic wave propagation, the induced electromotive force will be generated on the antenna oscillator under the action of the electromagnetic wave.When the antenna is connected to the receiving device, a high frequency current will be generated at the input end of the receiving device. In this way, the antenna plays a receiving role and converts electromagnetic wave into high frequency current. That is to say, the antenna plays the role of receiving antenna. The receiving effect depends not only on the direction of the antenna, but also on the matching of the half-symmetric oscillator with the receiving equipment.

　　Whether it feels particularly abstruse, completely unable to understand the appearance, in fact, as long as you go to the manufacturer of electronic antenna hands-on test will find that it is still very simple.