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What should be paid special attention to in the design of antenna shrapnel?
1、 Motherboard
1. When wiring associated with RF, special attention should be paid to using a 45 degree angle or arc treatment at turns, and ground paving protection and characteristic impedance simulation of wiring should be done well. In addition, the RF ground should be designed reasonably and effectively. The reference ground plane for RF wiring should be found correctly, and the signal return path should be ensured to be the shortest when RF signal wiring, and the corresponding layer between RF signal wires and ground should not be affected by other wiring. The boundary between the board and the ground should be marked with a "ground wall". The antenna feed microstrip line led from the RF control module of the PCB circuit board should not be placed in the middle layer of the PCB circuit board to prevent the characteristic impedance of the line from being uncontrollable and reduce losses. It is advisable to design it on the TOP surface, and the reference layer should be a complete reference plane. And at the junction with the shielding box, the shielding box should be designed with slots and bypasses to prevent short circuits and bypass coupling.
2. Protect the surrounding area of the RF control module from scattered unshielded parts, and minimize the opening of heat dissipation holes. The most taboo is the elongated hole groove. The projection area of the mobile phone antenna shrapnel has a complete ground pavement, and it is best not to distribute components on the antenna side, especially parts containing metal components, such as audio speakers, motor motors, camera substrates, and low-frequency drive components, to be grounded as much as possible. These have a significant negative impact on the electrical characteristics of antenna shrapnel
3. The spatial radiation of antenna shrapnel will be coupled and absorbed by the metal parts of the motherboard (including the metal component decorative parts around the antenna on the chassis), resulting in a certain amount of secondary radiation. The frequency is related to the size of the metal product. This can lead to a certain level of noise in the entire machine, which is also related to the series resonance pairing control circuit between the antenna and RF control module. If the stability performance of the series resonance pairing control circuit is poor, it is easy to excite disturbances that generate higher-order harmonics. Therefore, it is stipulated that such parts have good grounding to eliminate or reduce secondary radiation.
2、 Design of the casing
Because the built-in antenna shrapnel on a mobile phone is relatively sensitive to the conductive medium around it, the design of the phone shell is inevitably related to the antenna characteristics. The surface coating material of the shell should not contain metal components, and it is best not to design any metal decorative or electroplated parts near the periphery of the shell near the antenna. If necessary, non-metallic processing techniques should be used to achieve this. The conductive spraying on the inner side of the casing should stop at a distance of 20mm from the antenna. For pure metal battery covers, they should be at least 20mm away from the antenna. If a monopole antenna is used, it is prohibited to use metal shells and circular metal decorations on the panel. The distance between the battery (including the electrical connection base) and the antenna should be designed at least 5mm.