Question about chip antenna placement on a PCB

[paul0208]

Hi,

I’m planning to use a chip antenna that meets the attached specifications.
I’m not very familiar with RF hardware, and I’ve only just started using CAD.
I placed it according to the specifications, but I’m not fully confident about the layout.
Could you please review it?

A CR2032 battery will be mounted on the back side.
For additional RF tuning between L2 and the chip antenna, is an additional pi-network required?

BR
Paul

[Bendik Heiskel]

Hi Paul,

The layout of the antenna looks OK

For additional RF tuning between L2 and the chip antenna, is an additional pi-network required?

 L1, L2 C3 and C4 are the radio matching and filtering circuit, it can not be used for antenna impedance matching.

From the snippet from the antenna datasheet you can see that a Pi network consisting of 2 shunt capacitors and one inductor is recommended:

As a starting point the capacitors can be NC/DNP while the inductor can be replaced by a 0 Ohm link. The values of these components must be determined after the board is produced and the impedance of the antenna is measured using a VNA.

 

A CR2032 battery will be mounted on the back side.

Where is the battery placed in relation to the antenna? Is it directly behind it?

 

Best regards,

Bendik

[paul0208]

This is bottom side.

[Bendik Heiskel]

This battery placement should be OK, since it is not within the antenna keep out area.

[paul0208]

This is for central, nRF52833.
I wonder it looks good for matching also.

Line width is 0.762mm, two layers, as your ref design.

BR
Paul

[Bendik Heiskel]

The line width for a 50 Ohm transmission line  is dependent on the thickness and dielectric properties of the PCB substrate, both of these parameters you can get from your PCB manufacturer. The width can be calculated using tools like AppCAD or Saturn PCB Toolkit, note that this type of transmission line is called a grounded coplanar waveguide. Some PCB manufacturer can also calculate the width of the trace for you to suite the substrate being used.

 

The matching network C315, L303 and C316 isn't needed, The SMA connector and the external antenna both have a impedance of 50Ohm already, so as long as the transmission line from the connector to the end of the radio matching network(in this case L302) also have an impedance of 50 Ohm there is no need for the matching circuit.

 

Other than this the layout looks good.

Best regards,

Bendik