CC2540 board thickness effect on antenna

Hi,

Could you provide the schematic of your design?

Changing layers stackup will have an impact on impedance matching between a balun and antenna.

Hi Igor,

The schematic for the parts between the CC2540 and antenna are identical to the reference design. The antenna is also identical. Regarding stackup, it's a two layer board 0.1mm thick. I resized the trace between the balun and antenna by calculating the microstrip impedance of the reference design and ensuring it was the same for the two layer thinner board.

It's now 3.4mil thick.

Well, I believe it's more complicated than just calculating the microstrip impedance.

Refer to AN0068 document for more info.

Also there is AN0098, but the link to it is broken, therefore I've attached it to this post.

0647.swra367.pdf

Daniel,

Just out of curiosity, what antenna are you using?  If it's a COTS, SMT antenna, doesn't the vendor provide layout guidelines?  

BTW, 4 layer RF PCB's are nice because you then have internal ground plane layers.  Do you not have room for a 4 layer PCB or is the issue cost?

Regards,

Eric Hooker

RF Consultant 

Thanks for the replies Igor/Eric.

The antenna is a PCB IFA antenna as in AN043. The only mention of a different thickness PCB is the line "To
compensate for a thicker/thinner PCB the antenna could be made slightly shorter/longer".

We've recently tested the board and obtained about 9m range (line of sight) as opposed to about 11m for the original board. Part of that is possibly attributable to the fact the 0.1mm board uses 1/3oz copper.

The reason for a 2 layer board was sharp constraint on board height.

Regards,

Daniel

Daniel,

Thanks for the post and I looked at AN043.  If you have a planar EM simulator such as Sonnet or Axiem then the antenna could be modeled and optimized for your PCB design.

Regards,

Eric

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