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I am designing a GPS module using the following chip antenna:

https://product.tdk.com/en/system/files?file=dam/doc/product/rf/rf/antenna/catalog/rf_ant_ant161575st-1202a1_summary_en.pdf

The datasheet recommends routing the antenna like this:

enter image description here

The long "L" shaped trace coming out of the antenna is connected to GND. What I don't understand is the vias. The datasheet says the antenna is to be placed over an area 5mm x 6mm with no copper beneath it. So what I don't understand is:

  1. Where are those vias going?

  2. How am I supposed to connect it to GND if I don't have any copper beneath it?

Unfortunately the datasheet doesn't provide much info and I am a total noob at designing for RF. I am pretty sure all the other vias you see on the image are part of a large GND pour, which are surrounding the feed trace from the antenna. I guess that is to shield the feed trace? Any help anyone can give here to help me understand how to get this design right the first time would be greatly appreciated.

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    \$\begingroup\$ where is "The datasheet says the antenna is to be placed over an area 5mm x 6mm with no copper beneath it" in the linked document? \$\endgroup\$
    – Kartman
    Apr 17 at 4:24

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The L-shaped trace coming from the "Radiator Electrode" pad of the ANT161575ST should not be grounded. In fact, I'd consider that trace to be the antenna, and the chip itself to be mostly a matching network.

The datasheet isn't great on details, but the VIAs suggest to me that there is an L-shaped trace on the PCB back that matches the L-shaped design on the front. The gray area is the "antenna keep-out" meaning no other traces or ground planes in that 6 x 5 mm area. I believe in their "Evaluation Board" the entire back side, except for the keep-out area, is to be copper pour used as a ground plane.

Their antenna pattern measurements are only accurate for an 80 x 10 x 1 mm PCB. If your PCB has a different profile, expect the pattern to change, but if it's at least a quarter-wavelength long (about 50 mm) your antenna should work acceptably but with reduced efficiency.

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  • \$\begingroup\$ Thanks so much for your response. I don't remember where I saw online that the radiator electrode pad should be connected to GND but I guess it must have been wrong. I will make it it's own net and connect the trace as you recommended. As a follow-up, my understanding is that the other pad labeled "Feed Point" on the datasheet is the trace that runs to the LNA and SAW filter before going to the GPS receiver's "RF IN" pin. Have I at least understood that part correctly? \$\endgroup\$ Apr 19 at 14:12
  • \$\begingroup\$ @humanistscience yes, the "Feed Point" connects to your RF front end components. Also, some additional info here: product.tdk.com/system/files/dam/doc/product/rf/rf/antenna/… \$\endgroup\$ Apr 19 at 15:46

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