Thingy 91 - antenna efficiency

[lobaro-theo]

Hello,

i was wondering about the stated antenna efficiency here:

infocenter.nordicsemi.com/index.jsp

The very poor values (< 20%) provided for the efficiency do not fit to the stated VSWR < 3:1 which translates into at least 75% antenna efficiency. 

Thanks for a clarification of the documentation.

Best regards,

Theo

[lobaro-theo]

see "antenna performance"

[lobaro-theo]

okey it seems that the answer might be that you have significant losses in the matching network 

[ketiljo]

Hi Theodor

Sorry for the late answer, the office has been closed due to Easter. 

SWR is not the same and not at all related to the antenna efficiency. SWR tells you the ratio between how much power that is absorbed by the antenna but not how the antenna is able to radiate this power. For small boards, where the ground plane the antenna sees is small, the efficacy of the antenna will be less than for boards where the antenna have a larger ground plane. The lower the frequency, the larger the ground plane is needed to maintain the antenna efficiency.

So even of you are able to perfectly match the antenna with a very low SWR, the efficiency can be very low if the antenna isn't able to radiate the power. For instance, a 50 ohm resistor will have an SWR of 1:1, but extremely low efficiency. 

best regards,

Ketil Aas-Johansen