About WiFi antenna design
About WiFi antenna design
With the intensification of market competition, hardware devices are developing in the direction of integration. The antenna has also evolved from an external evolution built-in to
Embedded, let's first introduce the types of antennas for this type of application:
⑴ On Board: It adopts PCB etching and integrated molding, with limited performance and extremely low cost. It is used in Bluetooth,
WIFI module integration;
⑵ SMT mounting type: materials are ceramic, metal sheet, PCB, performance and cost are moderate, suitable for mass embedded radio frequency
Module
⑶ IPX external: using PCB or FPC+Cable combination, excellent performance, moderate cost, widely used
OTT, terminal equipment;
⑷ External: Plastic rod antenna, high performance, independence, high cost, applied to terminal equipment, no need to consider
Consider EMC and other issues;
The ultimate purpose of the antenna is to radiate radio frequency signals into free space. At this time, the design of the antenna is very important, but
The antenna design largely depends on the characteristics of the installed platform. In addition, the antenna is very sensitive to the surrounding environment. These reasons lead to
In many cases, the antenna is a unique design for each platform. Due to the customer's consideration of antenna design
I’m not quite sure, here are some suggestions we have on the design of portable device antennas, so that customers can better design themselves.
The circuit and PCB increase the chances of project success. But each project has its own characteristics, so there are some questions
Questions need specific analysis of specific issues
Wi-Fi antenna requirements for PCB layout and structure
1. Antenna form, antenna location and feed point size recommendations
The built-in antennas often use several forms, which are divided into shrapnel form, chip patch antenna and FPC antenna. Patch
The form of the antenna is uniform and has a fixed size. The position and size of the pad are also fixed according to the specific specifications of the antenna.
Fixed. In addition, according to specific types of antennas, there are design guidelines such as related clearance requirements around the antenna and recommendations for equipment size.
Guide opinions.
If the form of shrapnel is adopted, we recommend that customers use PIFA antenna as the form of WiFi antenna. According to our experience
Test, PIFA antenna success rate and performance are better. The antenna RF feed pad should be 2×3mm in size, and the pad
There is no copper on all layers of the PCB with a peripheral area ≥ 0.8mm. If it is a PIFA antenna, add a 2×
3mm ground pad, the distance between the two pads is 2mm.
The antenna is usually located at the top of the device, starting from the top of the PCB, cut off the ground of all layers in this area 2～
3mm, but the pad part of the layer that belongs to the antenna ground pad should be reserved.
Note: The area in the yellow box is where the antenna and bracket are installed.
2. Recommendations for matching circuit wiring
antenna
The topological structure of the matching circuit is from the antenna to the test port or Power amplifier. match
Do not lay the ground under the distribution circuit and in the 1.5mm area around the matching network. The matching network is placed at a distance from the feed pad
It is better to put it closer (but not too close).
3. Microstrip line from WiFi module to antenna matching circuit
The signal transmission line from the WiFi module to the antenna matching circuit is a microstrip line with a characteristic impedance of 50 ohm. In order to avoid
With line loss, the module should be as close as possible to the antenna. The size of the microstrip line must be determined according to the specific PCB.
Crossing lines are not allowed to pass between the microstrip line and ground.
4. Some other issues
Grounding: A good RF grounding is undoubtedly very important for the wireless performance of a mobile phone. The following designs must be followed
in principle:
Try to make the ground in the outer area as complete as possible and not be damaged by segmentation (the part inside the non-shielding cover). This is for the area near the antenna
Region is particularly important. The antenna current must be isolated from the noise current, if the grounding area near the antenna is broken into incomplete
It is necessary to produce a filling ground plane in the relevant area below it, and stitch it with ground vias to make it a complete
Ground. The wiring in this area must ensure that the antenna current only flows through the surface plane, and the noise current must be restricted from flowing into the complete ground inside.
flat.
When using a pre-produced antenna, it is important to note that its characteristics depend on the ground plane to which it is connected. Only when the ruler of the ground plane
When the size and shape are consistent with the manufacturer's evaluation board, the manufacturer's marked specifications can be reached. In other cases, use
The user needs to measure the impedance of the pre-produced antenna under actual application conditions and match it to the required characteristic impedance.
5. The use of metal components of the equipment shell
Do not use spraying or plating with metal components on the surface of the shell. The metal plating cannot achieve reliable grounding.
Antenna performance has a great impact.
Do not use metal decorations near the antenna.
6. Use of pure metal structural parts
When using all-metal components (such as front panel or rear panel), please reserve multiple grounds for the components used
The location of the specific grounding point is determined by the antenna design company.
There should be no grounded or ungrounded metal decorations above the antenna radiation area, including electroplating and gold plating.
7. Consideration of reserving installation location for antenna
The antenna should be installed far away from metal objects, and the antenna needs enough space to unfold. If a chip antenna is used, it needs
In accordance with the requirements of the application guidelines, provide sufficient clearance area and corresponding size of the ground.
If a shrapnel antenna is used, a support should be designed for the antenna, the antenna is fixed on the support, and the support and
The PCB is then fixed; or without the bracket, the antenna is fixed on the shell.
When designing the structure, consider the space and location of the antenna installation, and consider installing the antenna on the bracket or
A hot melt column is added to the shell to fix the antenna.
8. Consideration of the relative position layout of other modules and antennas
For speaker, camera, vibrator, LCD, battery and other components and the relative position of the antenna, here are some
The usual suggestions:
The antenna should be far away from the camera and flexible PCB;
The antenna must be at least 5mm away from the battery;
Keep the Vibrator away from the antenna;
The minimum distance between the antenna and the shield is 2-4mm (it will cause parasitic effects);
RF switches and amplifiers or duplexers should be as close as possible to the matching circuit area.
