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I have looked online a bit and it seems to me that the general belief is that the larger the ground plane (up to a certain extent), the better.

I am trying to design a patch antenna, so I ran several full-wave simulations and increased the ground plane size each iteration, extracting the gain. I observed that as I increase the ground plane size, the gain increases at first and then decreases. Additionally, I've read a paper which claimed that the gain of the antenna changes periodically with the ground plane size.

Does anyone with experience relating ground plane size to antenna gain know of any useful resources?

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  • \$\begingroup\$ How did you measure the gain of the antenna? \$\endgroup\$ Commented May 28, 2017 at 8:30
  • \$\begingroup\$ It's extracted from a full-wave simulation \$\endgroup\$ Commented May 28, 2017 at 14:51
  • \$\begingroup\$ How are you feeding the signal into the antenna? \$\endgroup\$ Commented Jun 17, 2017 at 20:00

1 Answer 1

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I am no RF expert, but I do know as you change the ground plane size you change the field distributions at the edge of the antenna.

Thus, if you keep your feed point in the same spot the impedance will have changed due to the field distribution change. Because the impedance changes, the antenna will no longer be in the sweet spot (the 50 \$\Omega\$ spot), meaning that it will suffer impedance mismatch loss.

Therefore, as you increase the size of your ground plane, you need to redetermine where to feed the signal so as to minimize impedance mismatch loss.

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  • \$\begingroup\$ In general, this is not true. The modal field distributions can change as ground planes get smaller, but once they're large enough, assuming you don't excite a surface wave mode, the field distribution will stabilize.For a patch, the impedance typically varies as cosine-squared along one of the symmetry axes; you want to excite it where you maximize mode-coupling between the probe and the patch, i.e. at the 50-ohm point. \$\endgroup\$
    – AntennaGuy
    Commented Jul 18, 2017 at 19:44
  • \$\begingroup\$ The general rule-of-thumb is to have at least one wavelength behind the patch to reduce any edge currents on the ground plane. The ideal patch is unbalanced, so you should have most of the surface current distribution on the patch surface. Once your ground plane gets large enough, the finite ground plane effects should be negligible. \$\endgroup\$
    – AntennaGuy
    Commented Jul 18, 2017 at 19:47

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