Several suggestions for PCB layout and structure of WiFi antenna design

Several suggestions for PCB layout and structure of WiFi antenna design

The ultimate goal 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 is largely dependent on the characteristics of the installed platform, and 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. Because the customer’s consideration of antenna design is not

It’s too clear. Here are some suggestions we have on portable device antenna design, so that customers can better design their own electronics.

Road and PCB, increase the chance of project success. But each project has its own characteristics, so there are still some questions that need to be

Analyze specific issues.

1 Some suggestions for PCB layout

1.1 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. paste

The form of the chip antenna has a uniform specification, and has a fixed size. The position and size of the pad are also fixed according to the specific specification of the antenna.

Fixed. In addition, according to the specific type of antenna, there are related design guidelines such as clearance requirements around the antenna and equipment size recommendations.

opinion.

If the form of shrapnel is adopted, we recommend that customers use PIFA antenna as the form of WiFi antenna. According to our

Experience, the success rate and performance of PIFA antennas 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’s a PIFA antenna, add a 2×3mm

The 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.

1.2 Recommendations for matching circuit wiring

The topological structure of the antenna matching circuit is from the antenna with four pieces in series and parallel to the test port or Power

amplifier. Do not lay the ground under the matching circuit and in the 1.5mm area around the matching network. Matching network placement distance

It is better to place the feed pad closer (but not too close).

1.3 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. Do not

Allow crossed lines to pass between the microstrip line and ground.

1.4 Some other issues

Grounding: A good RF grounding is undoubtedly very important for the wireless performance of mobile phones. The following settings must be followed.

Principles of calculation:

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 vicinity of the antenna

The area is particularly important. The antenna current must be isolated from the noise current, if the grounding area near the antenna is destroyed as incomplete

If it is, a filling ground plane must be generated in the relevant area underneath and stitched 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 plane inside.

When using a pre-produced antenna, it should be noted that its characteristics depend on the ground plane to which it is connected. Only when the ground plane

When the size and shape are consistent with the manufacturer's evaluation board, the specifications indicated by the manufacturer 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.

2 Some suggestions on industrial design

2.1 The use of the metal component 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.

It has a great impact on antenna performance.

Do not use metal decorations near the antenna.

2.2 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.

2.3 Considerations for reserving installation positions for antennas

The antenna should be installed far away from metal objects. The antenna needs enough space to unfold. If a chip antenna is used, then

It is necessary to provide sufficient clearance area and correspondingly sized ground in accordance with the requirements of the application guide.

If a shrapnel antenna is used, a bracket should be designed for the antenna. The antenna is fixed on the bracket, and the bracket and PCB

Then fix it; or without the bracket, the antenna is fixed on the shell.

When designing the structure, it is necessary to consider the space and location of the antenna installation, and consider the mounting of the antenna on the bracket or

A hot-melt column is added to the housing to fix the antenna.

2.4 Consideration of the relative position layout of other modules and antennas

For the relative position of the speaker, camera, vibrator, LCD, battery and other components and the antenna, here are some tips.

Chang's suggestion:

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