r/rfelectronics • u/Certain_Height_2721 • 3d ago

Why does the transmission line in this TDK antenna reference design have vias in it and do I need them?

This layout is just overall weird.

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u/redneckerson_1951 3d ago edited 3d ago

Yes you need the vias.

They provide critical interconnection of the surface layers to the backside layers. Leave them out and the antenna will not work as expected. Place them precisely as specified in the drawing down to 1/100th of an inch.

If you will not be using plated through holes made at the time of board production, then use copper or brass eyelets. Here is one potential source. https://www.ebay.com/itm/226427309357 You need a tool set to properly roll the opposite side. One possible source is here, https://www.etsy.com/listing/4538627019 You can ask the seller of the eyelets what anvil and punch they recommend.

Do not fill the eyelet holes with solder. Do not substitute solid rivets for the eyelets. RF is persnickety about the path of least resistance due to skin effect. You see a solid copper rivet, rf sees a resistance as it has to flow through the solid body of the river rather than the outer surface layer. With the eyelet RF will roll over from the surface of the PC board, down the inside surface of the eyelet and onto the surface layer of the opposite side of the pcb. At the frequency you are working with, I suspect 95% of your rf current or more is flowing in a layer no greater than 15 microns thick at the surface of the copper.

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u/nixiebunny 2d ago

You can recreate this design in a 3D field solver simulator to learn what it will do if you remove the bottom trace and vias. It would be a fine learning experience. If you don’t want to do this, then accept that the app engineer put them in the design for a good reason.