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Inverted F antenna questions

Emil Eriksson70652
Prodigy 130 points
Other Parts Discussed in Thread: CC110L

Hello,

I'm interested in using one of the PCB antennas provided in TI design documents, the Inverted F Antenna in DN0007 (http://www.ti.com/lit/an/swru120b/swru120b.pdf). However, I have a few questions:

  • Can I connect the feed point directly to the 50 ohm feed line from the reference design? That is, can I replace the SMA connector in the reference design with this antenna? Is it okay to make turns in this feed line if just using a straight line is inconvenient? I'm assuming I should avoid 90 degree turns, of course.
  • How much impact does the antenna-to-board-edge distance have on performance? I'm thinking about the H4 measurement.
  • The design note for the Inverted F Antenna states that if the board is wider than the antenna, then care should be taken to not place components close to the antenna. Does this apply to mounting screws (not connected to ground) as well?
  • Should the antenna be covered with solder mask.
  • From what I've read elsewhere, the ground plane is actually part of the antena so there needs to be a continuous ground plane edge along the whole width of the antenna, am I right?
  • 0
    TI__Mastermind 33160 points

    Hi Emil,

    The feed point can be directly connected to the 50 ohm connection. Always a good idea to add a pi-network so the antenna mismatch losses can be kept to a minimum.  The connecting feedline to the antenna should be 50 ohm and this track to the antenna can be meandered (see ref design for CC110L as an example). The board edge distances is not too sensitive (H9) but the distance / thickness of the track (H4) should be copied.

    If you will be having a wider board then the ref design, then try to keep all other components within the GND plane region. All components / object placed in the near vicinity of the antenna  will effect the matching and the resonant frequency. This is why it is always a good idea to include a pi-filter for matching purposes and if the antenna has a good match then a 0 ohm resistor can just be used. Antenna should be covered with a solder mask.

    The GND plane is a part of the antenna and varing the GND plane size will effect the resonance. Best practice to keep a solid GND plane along the edge of the width of the antenna.

    Regards,

        Richard.