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'[EE] Ground plane under a GPS antenna.'
2008\06\21@221443 by Alexandre Guimar„es

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       I have a board that has a 25 mm patch GPS antenna and the datasheet
states that the antenna gain is dependent on the size of the ground plane
underneath it. I have space to make the ground plane bigger but it would
become "irregular" in shape. I looked all over and could not find
information if making the ground plane not square would have impact in the
antenna directivity or affect it in some other "funny" way :-(

       Does anyone know if it is better to stick to a rectangular ground
plane ?? Google did not help on this one :-(

Best Regards,
Alexandre Guimaraes

2008\06\22@075448 by olin piclist

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Alexandre Guimarães wrote:
> Does anyone know if it is better to stick to a rectangular ground
> plane ??

Anything less than infinite is a compromise.  About 1 wavelength radius is
"good enough" for most practical cases.  Circular is the best shape because
that guarantees the highest minimum distance to the edge of the ground plane
while using the least area.

Anything less starts effecting the gain, radiation pattern, impedence, and a
bunch of other parameters that even fancy modeling software will only give
you a rough idea about.  How much that matters depends on your application.

Embed Inc, Littleton Massachusetts,
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\06\22@150555 by Vasile Surducan

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For a GPS receiver you need an overall gain (receiver + antenna) of
about +150...160dB. If you have a 25mm passive antena, the gain can't
be larger than +0...3dBi. On very few patch antennas the gain can be
as high as +7dBi.
So, admitting your receiver is a good one and you have +150dB gain, it
does not matter too much if your antenna has 0dB or +3dB gain...
What I try to tell, the ground size for a GPS antenna is really
important if you have an active antenna. As long you don't have one, a
ground size equal with the antenna size is not bad, no matter if it's
rectangular, circular or what ever...

On 6/21/08, Alexandre Guimarães <> wrote:
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2008\06\23@040944 by Vasile Surducan

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One more: The ground plane is important not only for the antenna gain,
but it's fixing the anthena characteristic (the S11) which can be
accidentaly moved with 50-200MHz above or below the 1575.42MHz. That's
why an antenna connected to a solid device is more stable than a
simple antenna with a PCB ground behind. Moving the hand behind the
ground plane surface is changing the S11 in a huge way.
I'm fresh with this because may last project is a GPS receiver (and
not conecting a NMEA output to a PIC which is not about GPS)

On 6/22/08, Vasile Surducan <> wrote:
{Quote hidden}

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