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Ante Micro Intelligent Communication (Shenzhen) Co., Ltd.
Requirements of Wireless Antenna for PCB Layout
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Release time:
2021-09-08 18:00
1. Suggestions for the form of wireless antenna and antenna location and feed point size
The built-in antenna is often used in several forms, which are divided into shrapnel form, chip patch antenna and FPC antenna. The form of the patch antenna is uniform and has a fixed size, and the position and size of the pad are also fixed according to the specific specifications of the antenna. In addition, according to the specific model of antenna, there are design guidelines such as relevant antenna clearance requirements around the antenna and recommendations for equipment size. If it is in the form of shrapnel, we recommend customers to use PIFA antenna as the form of wireless antenna, according to our experience, the success rate and performance of PIFA antenna are better. The antenna RF feed pad should be 2x3mm in size, and the pad should be ≥ 0.8mm area below the periphery, and no copper should be distributed on all layers of the PCB. If it is a PIFA antenna, a 2x3mm ground pad is also added, and the distance between the two pads is 2mm. The location of the wireless antenna is usually on the top of the device, starting from the top of the PCB, cut off the ground of all layers in this area by 2~3mm, but the pad part of the layer that belongs to the antenna ground pad should be retained.
Second, the wireless antenna matching circuit wiring suggestions
The topology of the wireless antenna matching circuit is to start from the antenna and connect four pieces in series to the test port or power amplifier. It is better to place the matching nets close to the feed pads (but not too close).
3. Microstrip line from WiFi module to wireless antenna matching circuit
The signal transmission line from the Wi-Fi module to the antenna matching circuit is a microstrip line with a characteristic impedance of 50ohm. To avoid losses on the microstrip line, the module should be as close to the wireless antenna as possible. Microstrip lines must be sized on a PCB-by-PCB basis. Crossing lines are not allowed to pass between the microstrip line and ground.
Fourth, the wireless antenna has a good radio frequency grounding
It is important to keep the outer area intact as much as possible and not to be destroyed by partitions (the part that is not inside the shield), which is especially important for the area near the antenna. The wireless antenna current must be isolated from the noise current, and if the ground area near the antenna is destroyed as incomplete, a block must be generated in the relevant area below it to fill the ground plane and stitched with ground vias, so that it becomes a complete ground. The traces in this area must ensure that the antenna current flows only through the surface plane, and that the noise current flows into the inner full ground plane must be restricted. When using a pre-production wireless antenna, it is important to note that its characteristics depend on the ground plane to which it is connected. The specifications indicated by the manufacturer should only be achieved if the size and shape of the ground plane are consistent with the manufacturer's evaluation board. In other cases, the impedance of a pre-produced antenna needs to be determined under real-world application conditions and matched to the desired characteristic impedance.