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C&T RF Antennas Inc
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WiFi antenna requirements for PCB layout and structure
Source:Original | Author:C&T RF Antennas Inc | Publish time: 2018-12-21 | 883 Views | Share:

Abstract: The internal antennas are often used in several forms, in the form of shrapnel and chip patch antennas and FPC antennas. The form of the patch antenna is of a uniform size, has a fixed size, and the position and size of the pad are fixed according to the specific specifications of the antenna. In addition, according to the specific model of the antenna, there are related design guidelines for the clearance around the antenna and the recommendations for the size of the device.

 

1. Antenna form and antenna position and feed point size recommendations

The built-in antennas are often used in several forms, in the form of shrapnel and chip patch antennas and FPC antennas. The form of the patch antenna is of a uniform size, has a fixed size, and the position and size of the pad are fixed according to the specific specifications of the antenna. In addition, according to the specific model of the antenna, there are related design guidelines for the clearance around the antenna and the recommendations for the size of the device.

If the shrapnel format is used, we recommend that customers use the PIFA antenna as the form of the WiFi antenna. According to our experience, the success rate and performance of the PIFA antenna are better. The antenna RF feed pad should be 2&3mm and the pad should have no copper on all layers of the area with 0.8mm. If it is a PIFA antenna, add a 2&TImes; 3mm ground pad with a distance of 2mm between the pads.

The antenna is usually located at the top of the device, starting at the top of the PCB, cut the ground of all layers in this area by 2 to 3 mm, but the pad portion of the layer belonging to the antenna ground pad is retained.

2. Suggestions for matching circuit wiring

The topology of the antenna matching circuit is four parallel strings from the antenna, to the test port or Power amplifier. Do not lay the floor under the matching circuit and within 1.5mm around the matching network. It is better to match the placement of the network to the feed pad (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 50-ohm characteristic impedance. To avoid losses on the microstrip line, the module should be as close as possible to the antenna. The microstrip line must be sized according to the specific PCB. Crossed lines are not allowed to pass between the microstrip line and the ground.

4. Some other questions

Grounding: Good RF grounding is undoubtedly very important for the wireless performance of mobile phones. The following design principles must be followed:

Try to make the ground in the outer layer intact and not be broken (the part inside the non-shield), which is especially important for the area near the antenna. The antenna current must be isolated from the noise current. If the grounded area near the antenna is broken into incomplete, a fill plane must be created in the relevant area below it and stitched with the ground via to make it 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 must flow into the complete ground plane.

When using a pre-production antenna, it is important to note that its characteristics depend on the ground plane to which it is connected. Only when the size and shape of the ground plane are consistent with the manufacturer's evaluation board can the specifications specified by the manufacturer be met. In other cases, the user needs to measure the impedance of the pre-produced antenna under actual application conditions and match to the desired characteristic impedance.

5. Problems with the use of metal components in the equipment casing

Do not use metal-coated spray or plating on the surface of the casing. Metal plating cannot achieve reliable grounding, which will have a great impact on antenna performance.

Do not use metal decorations near the antenna.

6. Use of pure metal structural parts

When using all-metal components (such as the front panel or the rear panel), reserve multiple grounding points for the components used. The specific grounding point position is determined by the antenna design company.

There must be no grounded or ungrounded metal decorations above the radiating area of the antenna, including plating and gold plating.

7. Consideration of the installation location for the antenna

The antenna should be installed away from metal objects. The antenna needs enough space to deploy. If the chip antenna is used, it is necessary to give enough clearance area and corresponding size according to the application guide.

If a shrapnel antenna is used, the antenna should be designed with a bracket, the antenna fixed on the bracket, and the bracket and the PCB fixed again, or the antenna is fixed on the outer casing without the bracket.

Consider the space and position of the antenna installation when designing the structure, and consider adding a heat-melting column to the bracket or the housing to be mounted to fix the antenna.

8. Consideration of the relative position layout of other modules and antennas

For the relative positions of speakers, cameras, vibrators, LCDs, batteries, etc. and antennas, here are some general recommendations:

Keep the antenna away from the camera and flexible PCB;

The antenna must have a distance of at least 5 mm from the battery;

Vibrator should stay away from the antenna;

The distance from the antenna to the shield is a minimum of 2-4 mm (which can cause parasitic effects);

The RF switch and amplifier or duplexer should be as close as possible to the matching circuit area.