Newbie workflow suggestions for non-standard antenna design


#1

Hi! I am just getting started with KiCAD (and EDA period). Naturally my first project is not the standard pile of resistors and ICs, but a patch antenna with an SMA connector. I am having trouble filling zones and connecting them to the relevant traces. Perhaps someone can walk me through the basic approach (zones may not be the right one).

Design elements:

  • large copper rectangle (or more than one) on the front
  • connected together by traces of well-controlled width AND length (sub-millimeter control needed)
  • trace going to center pin of SMA and connecting patches
  • SMA mounted on back; through holes protruding to front (found and added footprint successfully)
  • ground plane on entire back
  • pads all around back side SMA for solid solder connection to ground plane (through legs soldered to pads on front just for mechanical strength)

Should I be using filled zones? Should the zones be on the net associated with the SMA central pin? Why don’t they fill (have gotten them too, unpredictably, unrepeatably)? Can I do trace length fine control? How do I customize the rear-side SMA solder pad interface?

I feel like I’m asking for things that simply may not be supported, but new to EDA, I can’t know for sure. Appreciate any advice!


#2

It sounds like what you are attempting is possible with KiCAD. However, KiCAD doesn’t actually support this kind of design work so there will be some workaround and sleight-of-hand as you coerce it into performing some unnatural acts.

You may find it easier to create the antenna as a footprint, rather than a circuit. Each patch would be defined as an SMT pad (or group of overlapping pads). Likewise for the transmission line elements. You may have to define separate footprints for the topside and bottom side geometries.

Can you post a sketch, dimensioned drawing, or even a screenshot (from, e.g., Sonnet) of your antenna design?

Dale


#3

Thanks for the quick response and advice. I had wondered if custom footprints would be the way to go; but fuzzy on what “device” I would attach to.

I did manage to trick it and got closer to my goal: I made a test point, associated with a large SMD pad footprint, so I was able to run a trace from the SMA center pin to the test pad, controlling the width of various transmission line segments along the way. Then I was able to draw zones on top of the transmission line and they filled in. The only problem is the clearance around the test pad within one of the zone/patches (picture below). I would like this to be filled in with copper, and also do not want soldermask exclusion around this pad (but do want it around the SMA pads).

So it seems I have a track getting me partway there. Still no proof of concept that I can carefully control exact dimensions of zones, or trace length. But I’m assuming I can work/figure these things out.


#4

If you have masochistic inclinations you can see the locations of the fill zones (shown in millimeters, out to 8 or 10 decimal places) by opening the *.kicad_pcb file in a plain-text editor such as “Notepad++”.

A more practical approach is to zoom in on each vertex in the zone, place the cursor, and read off the (X,Y) co-ordinates from the bottom-most ribbon bar on your display window. I think it’s a VERY good idea to condition yourself to make liberal use of the Relative Coordinate feature (activated with the bar).

[quote] . . . The only problem is the clearance around the test pad within one of
the zone/patches (picture below). I would like this to be filled in
with copper, and also do not want soldermask exclusion around this pad
(but do want it around the SMA pads). . . . [/quote]

The “Edit” dialog (or is it called “Properties”?) for each pad allows you to set things like solder mask on/off, fill-to-pad clearance, nature of pad-to-fill connection (you probably want “Solid”), etc. Some of these parameters can also be set for the entire footprint, and for the fill zone - I believe the pad-by-pad settings take precedence, but I’m not certain.

Dale


#5

I am precisely this sort of masochist: but VI editor–please… I am almost certain to embrace this approach.

[quote]
The “Edit” dialog (or is it called “Properties”?) for each pad allows you to set things like solder mask on/off, fill-to-pad clearance, nature of pad-to-fill connection (you probably want “Solid”), etc. Some of these parameters can also be set for the entire footprint, and for the fill zone - I believe the pad-by-pad settings take precedence, but I’m not certain. [/quote]

Good tips. I was able to eradicate the solder mask for this pad not by turning it off (did not find this option), but by making the clearance negative and larger than the pad half-dimension. Gone. Still have not managed to eliminate the cleared copper around the pad (Solid, None, Thermal, etc.; also tried negative clearance trick). But you’ve given me some ideas and I will continue to bang at it. Thanks!


#6

Loads of fiddling with no result, but then key was to “Fill Zone” again after making the changes. Now, ironically, as I try to determine what parameters control the gap (editing zone parameters, pad parameters, footprint parameters), I can’t seem to re-instate the gap even when unfilling and refilling. At least I have what I want.

Also, to correct a previous statement, I can turn off the solder mask by unchecking the mask layer in the Edit Pad dialog: no need to make negative clearances (though this works too).