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I'm struggling with antenna connections to GPS module in my PCB design.

My antenna is a smd passive patch antenna, "SGGP.25.4.A.02 from Taoglas". The antenna shape and recommended footprint is in the first two pictures. I'll be adding an antenna ground plane directly underneath the antenna.

I'm confused about the digital GND pads (1 to 9 in second picture) of the antenna connections. I'm guessing they need to be connected into the digital gnd layer I have on layer 2 through lots of vias with copper keepout regions between the ground pads and surrounding the feedline.

Is that correct?

The third picture is the only patch antenna layout I've managed to find from Abracon patch antenna application note but it's for an active antenna.

Their design is confusing me greatly and it doesn't seem right to me. They don't have an antenna gnd plane underneath the antenna.

I'm guessing the yellow region is a digital ground (separated from the ground of other components) and they're connecting the ground pads of the antenna to the ground of the GPS receiver through traces.

If I connect the gnd pads this way I'll have an interrupted antenna ground plane.

enter image description here enter image description here enter image description here

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You are struggling because the diagram you are looking at doesn't say anything about how to mount the antenna. Figure 9 is a GPS receiver with a connector for an external antenna.

Farnell has a datasheet for your antenna. This datasheet includes a layout for the test jig used in their tests of the antenna, as well as drawings that show how to design the footprint for the antenna.

This is (part) of the footprint:

enter image description here

It shows where the pads go, and where not to put a copper pour.

This is the test board:

enter image description here

It is 50mm by 50mm, and has a ground plane (copper pour) on front and back.

It has a connector so that you can run a cable to the receiver.

You'll want to lay out your board much like the example. You need to keep the 50mm square around the antenna clear of other parts, and you'll want to keep the ground planes as solid as possible.

Since you want to combine it with your receiver, you'll run a 50 ohm transmission line across your PCB from the antenna to your receiver. The transmission line can be on the front or the back.

The ground plane behind your antenna should be one piece with the ground plane under your receiver.

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  • \$\begingroup\$ Ok I seem to be confused between digital ground and antenna ground. Are the red pads 2 to 6 antenna ground planes in your figure? Do I ever need the digital ground for my antenna? \$\endgroup\$ – Maryam Magdy Jan 2 at 13:16
  • \$\begingroup\$ Digital ground has nothing to do with your antenna. That's a separate area, used for stuff like whatever microprocessor your device uses. Pads 2 to 6 all go to the same ground plane - that's the ground plane under and around the antenna. \$\endgroup\$ – JRE Jan 2 at 13:47
  • \$\begingroup\$ Get that "figure 9" out of your head. That's not your antenna \$\endgroup\$ – JRE Jan 2 at 13:47
  • \$\begingroup\$ Thank you so much. Figure 9 did mess with my head because it's a patch gps antenna so I thought it was the same! \$\endgroup\$ – Maryam Magdy Jan 3 at 5:41
  • \$\begingroup\$ I have another question please. What about the GPS receiver's ground? It is a digital ground but it better be separated from MCU's ground right? But shall it be separated from the antenna's ground on the second layer? In other words, How should I construct my ground on the second layer of the PCB? I will be having an antenna ground on the top layer directly beneath the antenna. \$\endgroup\$ – Maryam Magdy Jan 3 at 6:45

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