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I am new to RF electronics and trying to build my first circuit integrating Bluetooth Low Energy, with quite strong geometrical constraints : the whole thing needs to fit inside a narrow 8x5x60mm volume. I am thinking about using a chip antenna (e.g. Johanson 2450AT43A100) on one end of the PCB, but can't find information about the effects of having such a narrow ground plane : datasheets usually only present performance with large ground planes without saying much about the degradation we should expect if we shrink it below recommendations and theoretical limits related to wavelength.

Is there is any practical limit on the width of the PCB serving as the ground plane? For example, assuming proper tuning, should I expect a decent connectivity with this kind of antenna using a 7x40mm ground plane?

Notes:

  • The system is intended for short range communication only, with a device less than 2m away (possibly with a human body in the middle though).

  • I have seen interesting patch antennas like what Apple did for their Air Plugs, but I would really like to avoid the cost of a custom antenna design for now.

  • Another very interesting solution I found was Insight SiP ISP 1507. Sadly it's just a bit too large for our requirements...

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  • \$\begingroup\$ Those HC-05 bluetooth modules, as well as some of the ESP8266 boards, use pretty simple copper traces. \$\endgroup\$
    – JimmyB
    Jan 2, 2017 at 15:12
  • \$\begingroup\$ I forget the name, but there was a company making IMD chip antennas that worked almost irrespective of what kind of ground plane you had. \$\endgroup\$
    – Sam
    Jan 2, 2017 at 21:22

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you can use the Johanson 2450AT43A100 without the 50ohm feed line to reduce space and mount is as close as possible ti the output pin of the BT SoC. Because you are using a ground plane which is longer than a quarter wave length the only difference if you use a less wide ground plane is that the radiation polar diagram will be more of a donut shape this means that the antenna will have significantly higher gain on the sides than on the top/bottom. Please note that by referring to "the the Antenna" i mean the whole set including the ground plane. The antenna will behave as half wave dipole.

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  • \$\begingroup\$ I will try that and provide some feedback about the results. Thanks \$\endgroup\$
    – yoann-h
    Feb 25, 2017 at 8:14
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    \$\begingroup\$ I promised feedback quite long ago... Here it is: we ended up using a trace antenna on the long edge of the board with very good results (stable BLE connection for data streaming at over 50m in open field)! \$\endgroup\$
    – yoann-h
    Jun 26, 2018 at 16:31
  • \$\begingroup\$ Great news, I'm glad it worked. \$\endgroup\$
    – 555
    Jun 27, 2018 at 16:44

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