Arm Mbed OS support forum

Encapsulation of electronics (SX1276/1261 Shield) - antenna tuning

Hi everybody

We’re working with SX1276 and SX1261 mbed shields.
How much does encapsulating the electronics with epoxy resin affect the antenna tuning? Is there any experience?

Regards,
Manuel

RF would normally only be significantly be affected by metallic substances in the insulating material.
Epoxy resin in theory should not contain any, check the composition.
One way street though, once epox’ied its it the bin if you need get physical access to the PCB again :cry:

@star297 Thank you for your answer.
I didn’t mean the impact on the RF signal, but additional capacity trough the epoxy which could cause a shift in the antenna matching and thus reduce the TX power.

There is this publication if it helps:

Hello,

I know this is late, but perhaps still useful to someone, hopefully the original poster.

Adding anything to an antenna will alter the performance of the system the antenna is connected to.

Without knowing how the specific epoxy is made or details, I can say that it will definitely affect the match, the only real question is, “how much?”

It will affect the higher frequencies far more than lower. There are two main problems with using something like this.

The first is detuning. That means that it will make the transmission lines no longer 50 ohms. This will make it ok in some frequencies and worse in others. You can retune it, but usually the ability to retune a specific portion is narrow. Maybe this is ok if your band is only a small percentage of bandwidth.

The other issue is something usually referred to as the dissipation factor. This number determines how much loss there is. It’s not related to how much metal is present. It’s a property of the material itself. FR-4 has tolerable performance for most commercial uses upwards of several gigahertz for low power.

If you are only potting the boards and not the antenna, that is probably better. If you are potting the antenna too, you could have significant issues. You would have to test it. One of the most critical portions is where the antenna is fed, as you could end up shorting out some of the power. The effect is the same for receive and transmit, it will affect both the same way.

One way to test it, if you are just potting the electronics and not the antenna is to use a received signal measurement (assuming there is one) on an unpotted unit device. And then after it’s cured, test it after. That will be the most helpful. If you want to test it with potted antennas, you would need to be concerned that it would change the radiation pattern. If it only changed the pattern shape, then it could focus it, or cause the pattern to have weaker spots than before.

If you were to place the shield that appears like it could be there in the picture and then pot it (making sure that most of the epoxy stayed out of the shield) that would give you better performance.

Please let me know if you have any questions. I hope this is helpful.