Antenna system with decreased SAR value

A method for controlling SAR value of an antenna system, comprising steps as:

• (a) providing an antenna system, the antenna system comprising:
• a circuit board having a feeding point, an RF switch for making the antenna system work under a plurality of working modes with different frequency bands, and a system ground;
• a radiation body including a feeding portion electrically connected to the feeding point, a ground portion connected to the system ground by the RF switch, and a connecting portion connecting the feeding portion to the ground portion;
• the ground portion including a first half-sealed space formed by extending counterclockwise from an end of the connecting portion;
• the feeding portion including a second half-sealed space formed by extending clockwise from another end of the connecting portion;
• the ground portion including a first metal segment at a starting end thereof for connecting to the connecting portion, and a second metal segment at an ending point thereof;
• the feeding portion including a third metal segment at a starting point thereof and a fourth segment at an ending point thereof;
• the RF switch electrically connecting to the second metal segment, and the feeding point electrically connected to the fourth segment,
• wherein the RF switch includes a controlling chip and a plurality of peripheral circuits controlled by the controlling chip, and the antenna system connects to the system ground via one of the peripheral circuits, the peripheral circuit includes components connected in serial or in parallel, the components include at least inductance component, capacitor component, or resistance component;
• (b) when the antenna system works under one of the modes, adjusting topological structure of the peripheral circuit and values of the corresponding component, measuring the reflection coefficient curve of the antenna system and making a trapped wave of the reflection coefficient curve close to a center frequency of a predetermined working frequency band;
• (c) adjusting values of the components of the peripheral circuit, and making the trapped wave of the reflection coefficient curve move toward lower frequency or higher frequency;
• measuring radiation performance with SAR, and determining the values of the components when the radiation performance and SAR satisfies predetermined requirements;
• (d) repeating the steps (b) (c) when the antenna system works under another mode.