Antenna design for 4 Layer 1.0mm PCB

[Markus Aerni]

Hi

I am designing a new BLE device and have some questions about the PCB antenna.

The product will be worn on the body.

I have a 4 Layer PCB with 1.0mm with and 35u copper.

 

TOP        :              RF IC and components, RF trace, antenna, decoupling capacitors, and other signals

Inner 1   :              GND plane

Inner 2   :              VDD plane

BOT        :              GND and some signals

 

 

1. The antenna trace with should have 1.5mm right ?
2. What should be the distance from the GND planes to the antenna trace ?
3. should there be a GND plane under the antenna trace ? on what layer ?
4. should there be a GND plane under the components of the antenna network ?

 

Layout so far:

TOP

 

Inner 1 (GND plane)

 

Inner 2 (VDD plane)

BOT

Thanks a lot

M. Aerni

[ketiljo]

The antenna trace with should have 1.5mm right ?

A 1.mm wide track for the antenna will work fine.

What should be the distance from the GND planes to the antenna trace ?

At least 5 mm, but more than 10 mm is better. 

should there be a GND plane under the antenna trace ? on what layer ?

No, that will make the antenna useless. 

should there be a GND plane under the components of the antenna network ?

Yes, you will need to have ground under the matching network on the bottom layer (components between the ANT pins and the anetenna)

[Markus Aerni]

hmm i can do 3mm max. gnd distance on TOP and BOT layer.

is it better to remove the inner GND and VDD layer as wide as possible from the antenna ?
as shown in the Screenshot in the first poste

or does it not matter whether 2 or 4 layers are present at the antenna if they are well plated through with vias?

Thanks for your help.

[ketiljo]

3 mm will give you problems with the antenna being too capacitive. It doesn't matter what layer that's close to the antenna. It's the distance to the closest layer that matters.