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CC1101-Q1: Coplanar Waveguide Minimum Ground Widths

Zebryk
Expert 1240 points
Part Number: CC1101-Q1
Other Parts Discussed in Thread: CC1101

Hello,

When designing a coplanar waveguide without a ground plane, what is the minimum width of the Ground traces along side of the center trace?

All of the many CPW calculators that I have seen do not specify this.

Also, what is the best CPW calculator available in 2023?

Peace,

Jay Zebryk

  • 0
    TI__Mastermind 18435 points

    Hi Jay,

    For the CC1101 reference designs we use a continuous ground plane underneath the RF path so we do not recommend this; please follow our reference designs wherever possible to avoid performance deviations. The minimum width will depend on your PCB stackup, tolerances, ect.

    In case I'm missing some important information, what is the need for a CPW calculation in this context (assuming a CC1101 reference design is followed)?

    For calculators, either of these options produce good results:

    We removed the following App Note from TI.com several years ago as it was causing confusion for customers, but Section 4.3 could give you some useful information for adapting our reference design(s): /cfs-file/__key/communityserver-discussions-components-files/156/Adapting-TI-LPRF-Reference-Designs-for-Layer-Stacking-_2800_AN068_2900_.pdf

    Regards,

    Zack

  • 0 in reply to ZC
    Mastermind 6470 points

    In addition, I doubt that you have a long enough trace to be regarded as a transmission line. 

  • 0 in reply to ZC
    Expert 1240 points

    Zack,

    Thanks for the reply.

    However I was looking for more info about the width of the Ground Planes required.

    (Either the width of the Ground Plane below or the widths of traces along side.)

    Apparently, my specific application is serviced well by a Finite Ground Coplanar Waveguide (FGC).

    FGC - NASA

    Although not as optimum as an "infinite" Groundplane (which does not exist) these Finite Groundplanes can be very useful never the less.

    Peace,

    Jay Zebryk

  • 0 in reply to Zebryk
    TI__Mastermind 18435 points

    As TheGhostOf mentioned, the balun/filter matching section of the reference design is likely short enough to not be sensitive to many transmission line effects (as this is a Sub-1 GHz device). The only trace that potentially could be is 50 Ohm section after the LC filter to the antenna, depending on your design.

    Therefore, I am unsure why implementing a FGCPW structure would give any advantage over the reference design, particularly as by changing the layout you would likely need to tweak the impedance matching.

    Regards,

    Zack

  • 0 in reply to ZC
    Expert 1240 points

    This is a specialized application wherein I am feeding a mechanical dipole which is perpendicular to the board.

    From my research, I learned that the width of the lower ground plane in a co-planer waveguide can be as small as 2X the center feed without significantly increasing losses. This enables each side of the dipole to be fed using an upper and lower trace without any cross-over transition.

  • 0 in reply to Zebryk
    TI__Mastermind 18435 points

    Thanks for the additional context - sounds like an interesting application!

    Am I understanding correctly that you have found your answer yourself? If so, thank you for sharing.

    Regards,

    Zack