The designs I have seen all seem to have this surrounding stitched-to-the-ground copper pour surrounding them. Why put it on a differential antenna PCB like below ? And why are those thin lower left traces brought there for ?

EDIT: For the thin lower left traces question - what I wanted to ask is why are they not connected to a MCU, or, in case the pictured IC chip already contains a MCU, then why are they not terminated onto some external connector so the MCU can be programmed ?

MORE EDIT: The image below was taken from page 29 of http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=swra161b

enter image description here

  • $\begingroup$ Don't understand your second question, to be honest! The IC does something, and for that it might need some data/signal/clock/reference voltage/.... in- and output traces. Since these do not necessarily carry RF, the board designer doesn't have to design them to have a specific wave impedance at a specific frequency, and thus, these lines can be thinner. Not sure I'm actually answering your question regarding these lines, though... $\endgroup$ Apr 21 '17 at 7:14
  • $\begingroup$ @MarcusMüller clarified my qeustion $\endgroup$
    – kellogs
    Apr 21 '17 at 7:46
  • 1
    $\begingroup$ thanks! so, you mean the very lowest short trace on the left? It comes from the other side of the board, and goes back there (vias on both ends); there's some components on the flip side of the board! You're really asking us about the PCB layout of a board of which we neither have the schematic nor know what it does! $\endgroup$ Apr 21 '17 at 7:50
  • $\begingroup$ @MarcusMüller allright, more edits :) $\endgroup$
    – kellogs
    Apr 21 '17 at 11:03

The PCB shown here is a demo board, described in this TI application note.

Point is that all the components in the schematic (p.4) that are not on top of this design are on the bottom side – and that includes two sockets, one for power only, and one that seems to carry serial data.

Why the lines go from that bottom copper layer up to the visible side of the board and back down? Layout! Sometimes, it's impossible to connect two things without making two lines cross. So, you build a bridge by taking one trace to the other side of the board and then back after crossing the other trace.

For more info, you'd have to read that IC's data sheet, and the specification of the platform – someone certainly wrote down which pins on these (hidden) connectors do what, and the PCB designer had to live with that.

Generally, having a ground plane next to an unbalanced RF-carrying trace is a common technique – a coplanar waveguide. You're right, in this case, the majority of E-Field should definitely be happening between the two balanced traces, so that's not the motivation here.

If you, hower, look into the document linked above, you'll find this anotated photomask of the top layer:

copper layer

The text further up claims that the Dipole is already impedance matched, so that basically leaves geometrically practical aspects (you need have some sort of feed towards the antenna, and you don't want to start making funky non-rectangular ground pours, and if possible, the ground should be parallel to the dipole), aesthetics, and the fact, that, at least a little bit, the traces and components close to the RF pins on the IC might interact, so it's usually desirable to have them surrounded by ground.

  • $\begingroup$ great! just one thing - page 4 of that pdf does not indicate any feed to the antenna. And neither does the actual green board. Am I misunderstanding your point ? $\endgroup$
    – kellogs
    Apr 21 '17 at 16:43
  • $\begingroup$ a feed in this context is simply what connects the IC with the radiating part of the antenna $\endgroup$ Apr 21 '17 at 17:36
  • $\begingroup$ Oh, right. Hmm, would the feed be H1, H2, H3 or a combination between them ? $\endgroup$
    – kellogs
    Apr 21 '17 at 20:50

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