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GPS antenna question
Muku:
Hello, everyone! Hope you are all doing well in this tough times. I was looking at few gps ceramic patch antennas for my project.
This is an antenna by Molex. Now they have a detailed documentation on this. They have tested the antenna on different size ground planes and the output is below.
As you can see the 50mmx50mm ground plane has the worst return loss. Now supposed my application uses PCB the size of 50X50mm, does that mean this antenna is useless for my project?
If you are working with small sized PCB then how do you increase the size of the ground plane?
m98:
What's your target application? What does the environment of your PCB look like? Do you have any particular requirements for positional accuracy?
In general, if this is for a generic hobby project and you're pointing the antenna in the general direction of the sky, it will work perfectly fine. You might want to use a way more compact, omnidirectional SMD antenna instead, for example: https://www.mouser.de/ProductDetail/Antenova/SR4G013?qs=4NsIomN5445K9og%252BQVhwfg%3D%3D
cdev:
GPS, Beidou and Glonass use slightly different frequencies within that range.
The (kind of standard) taoglas 25mm patch GPS antenna works on a 50 mm GP but it does perform much better on a larger groundplane. The size of the groundplane as they point out does vary the way it resonates, significantly.
I use (two) antennas almost identical to that one in GPS applications that give a better idea of how well as GPS antenna is performing than most do. Both are taped to CD's because they work a lot better like that.
Just making it a bit larger improves its performance substantially. It works the best in the center of the largest piece of flat metal you can find.
This is generally true for all ceramic patch GPS antennas.
The smaller the GPS patch is the more critical tuning is and the less likely it is to cover all three GNSS constellations too - especially GLONASS, which is an outlier..
OTOH quadrifilar helix or similar designs dont require any ground plane at all, and are substantially more flexible in placement, which in some applications, such as a handheld unit thats not always going to have its top facing up, thats very important.
cdev:
Photos would help. As m98 says, it depends on how accurate you need it to be. A slightly larger ground plane will also make a big difference in a passive antenna situation, but it it has its own LNA, that will matter much less for having a GPS fix but that fix will jump all over the place if its non optimally placed.. Especially when the sky view isnt so great.
With any patch antenna, it needs to be resonating at the right frequency to work too. Using a patch antenna thats designed to resonate in the middle of a flat piece of metal on the end of a rectangular box isnt going to work well, unless its custom tuned to perform there.
amyk:
Look at the GPS antennas in smartphones. They are much smaller, yet work perfectly fine. It's all down to the sensitivity of the receiver.
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