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CC3235S: Chip Antenna: Length of Transmission Line

Robin Maeder
Intellectual 450 points
Part Number: CC3235S

Hello Everyone

I am making a 2.4GHz design with the CC3235S and the chip antenna RFANT5220110A2T. This antenna is recommended in the SimpleLink layout guidelines (document SWRU536).

In the datasheet of the antenna (page 3+4) it shows the recommended layout pattern and the design of the reference antenna. In both designs the transmission line to the antenna is pretty long. In the refercene antenna design it is dimensioned with 18mm. Also on the eval board LAUNCHXL-CC3235S the transmission line is pretty long. But my deisgn should be as small as possible. So in best case I would place the antenna really close to the CC3235S.

My question is if there is a requirement for the minimal length of the transmission line between CC3235S and antenna?

Thank you for your help.

Best regards Robin

  • 0
    TI__Mastermind 20800 points

    Hi,

    As long as you keep the trace impedance to 50 ohm you should be ok. It is recommended that you just copy RF portion of our layout as closely as possible in your design.

    Thanks

  • 0 in reply to FI
    Intellectual 450 points

    Hello

    Thank you for your reply. In the first sentence you say "SHOULD be ok", in the second one "RECOMMENDED to copy". That is exactly the information I am not looking for because this is the information I already have. Unfortunately it includes words like: should, could, most likely, recommended, probably...

    Don't get me wrong. I appreciate any answer to the topic but I am looking for a clear statement how the transmission trace length affects the performance compared to the reference design.

    Best regards

  • 0 in reply to Robin Maeder
    Guru 39650 points

    Hi Robin,

    Nobody can give you such statement, because it depends on your RF design including manufacturing of your PCB. Proper way is calculate your RF design and after that test your real design. Because RF design may to be affected even by your plastic enclosure. I hope that this tutorial give you important informations about crucial parts of RF design.

    Jan

  • 0 in reply to Hnz
    Intellectual 450 points

    Hi Jan

    Thank you for your answer and the link to the tutorial. Of course nobody can say that if the trace is xxx mm shorter the performance loss will be xxx %. That is not the information I am looking for. It is just about a statement of an RF experienced person regarding the impact/importance of the trace lenght. No guideline says something about this. So I am not sure if I can assume that the length is not really an important factor of the design.

    Best regards

  • 0 in reply to Robin Maeder
    Guru 39650 points

    Hi Robin,

    As was said above important is to have your path proper impedance. Length of of path is not that critical. Of course, shorter path is better, but in this case you may to have your antenna near to other components. And this can affect your RF performance. Without measurements at real prototype is hard to say how much this will affect your RF performance. After that you need select matching component to properly tune your antenna.

    Jan