Mobile phone antenna Principle

The antenna theory of the experts is simple: http://www.52rd.com/bbs/Detail_RD.BBS_187060_42_1_3.html




The problem must be analyzed in essence. The above two images can be used for analysis.
Antenna evolution can be analyzed by transmission lines. The transmission lines are represented by the same axis. The same axis is divided into core, insulation layer, and shielding network. When the complete Coaxial Line transmits high-frequency signals, there will be no electromagnetic radiation. When we strip the screen and expose the core line, there will be electromagnetic radiation when the alternating current passes through, when we open the core line of the same axis and the Screen Shield Angle, there will be electromagnetic radiation. When the angle reaches 180 degrees and the split part of the core line and the Screen Shield length is long, that is to say, it evolved into a dipolar antenna. the working principle of the dipolar antenna is not described here. other materials are described in detail. Now we can analyze the evolution of the dipolar antenna.
If the shield layer is connected to the main board, the core line is connected to the RF signal of the Main Board, and the open circuit end is perpendicular to the main board, the main board is equivalent to an arm of the dipolar antenna, that is to say, the motherboard can be regarded as a part of the antenna. In a limited viewing space, it is impossible to seek an infinite space. Under certain boundary conditions, the motherboard can be regarded as a ground, in this case, the model is monopole antenna (called Model A). If a monopole antenna is perpendicular to the main board, the other end is bent and parallel to the main board, it becomes an L-type antenna, that is, the radiation body of the antenna is close to the ground, which reduces the radiation resistance of the antenna. Because the input resistance of the antenna is small, a matching circuit must be added to match the impedance of the 50 ohm transmission line. The disadvantage of this antenna is that the spatial radiation direction and efficiency are not very good. If the motherboard is hollowed out, the effect will obviously improve. This is one of the reasons why the motherboard is usually hollowed out during monopole antenna.
On the basis of model A, a grounding part is added in the bending part parallel to the main board, which is called a flat inverted F-type antenna, that is, a PIFA antenna, which only carries a feeding tap) of the inverted L-type antenna, the grounding part is mainly used to adjust the impedance of the antenna.
The above is my understanding of the antenna. please correct me!