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I see requirements for specific ground plane sizes in many GPS antenna datasheets, but I also see many devices that ship with significantly smaller ground planes. Do these integrators know something that the GPS vendor doesn't, or am I missing something about the requirements?

As an example, u-blox SAM-M8Q Hardware Integration Manual specifies a 50mm x 50mm gp, but all off-the-shelf PCBs I see on the Web look much smaller (for scale, the M8Q patch is 15mm x 15mm).

SAM‑M8Q GNSS patch antenna module is intended to be placed in the middle of 50 x 50 mm GND size board, but a larger or smaller ground plane can be used. When using smaller than 40 x 40 mm ground plane, the performance may get decreased significantly.

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    \$\begingroup\$ The smaller ground plane will probably result in a less sensitive GPS. If I recall correctly, there is a table in the integration manual with expected sensitivity performance with different size ground plane. \$\endgroup\$ – Peter Karlsen Nov 2 '18 at 18:48
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It depends on the antenna, and the recommendations in their datasheets. I've used some with and some without ground planes (depends on the antenna construction). To figure out the best configuration, you'd have to build a PCB with both and test signal levels to see which is better. I don't have time/resources for that so I trust the manufacturer (sometimes). You could always rip the antenna apart, figure out what type it is (or whether the antenna has a built in ground plane) inside and simulate it, I don't have time for that either.

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