wiki/ news/ 2003-08-16 - Mock up CPA test using 0.005" PCB and 0.01" Copper and EPU

Who: Andrew

I tried mocking up a CPA with the new materials tonight.

The idea:

Outer surface: 0.005 in. thick "epoxy glass board". When measued with a calipers, it was 0.0055 in. thick, 0.5 oz copper. We'll etch the "inside" part of the board with the patch, so that the fiberglass backing protects it.
Dielectric: ~1/16 (0.0625) in. expanded (in place) polyurethane foam.
Inner surface: 0.010 in. thick copper sheet. Maybe use another piece of PCB material?

I had a polyethylene mold made out of two pieces of 1/2 in. thick polyethylene sheets. Even though they were thick, one was still clearly bent! Unbelievable.

Ground plane length on 5.25" airframe tube:

inner: 16.49336143


outer: 16.52477736


diff: 0.03141592

So I chose to make it slightly more than 16.5".

Radiator length on 5.25" airframe tube, and in 0.074" mold:

inner: 16.70856053


outer: 16.72583929


diff: 0.01727876

So I tried to make it about 16 23/32".

Width of patch and ground plane:

In terms of thickness: cpa_calculator_3.xls calculated a 2.422GHz, Er = 1.3 antenna patch to have a patch width (length, really) of 2.1370 in. Given the rule of thumb of 5x the dielectric thickness from any driven surface: (0.074 - 0.01 - 0.0055) * 5 = 0.292 in.

So:

spacing + patch + spacing + spacing + level 1 of corporate feed + spacing + spacing _ level 2 of corporate feed + spacing = 0.292 + 2.137 + 0.292 + 0.292 + 0.1929 (w_Zin) + 0.292 + 0.292 + 0.3134 + 0.292 = 4.3953 in

So I rounded it to 4.5".

Try number 1: Make yourself an antenna

  1. 0.010" copper foil is way, way too thick to cut with a razor blade.
  2. 0.005" 1/2oz double sided PCB is incredibly easy to cut with a razor blad.
  3. Don't tape BOTH sides down well. Duh.

  4. Pour A first. DO NOT MIX UP THE CAPS. Clean up the cap of "A" VERY, VERY WELL.

  5. There is only about 10 seconds of mixing time, MAX, before you HAVE to pour it, otherwise it's too goopy to drop down to the bottom of the mold.
  6. I used 1/2 oz A + 1/2 oz B and it was too little. It really should "pour" over the top so that we know it's reached all of the places in the mold.
  7. After about 10 minutes, it's completely skinned over.

Try Number 2: Screw the antenna, settle for the dielectric

  1. 1 oz + 1 oz seems just right. Next time, use 1.25 just to be safe.
  2. Measure out the quantities first, then pour into a larger cup.
  3. Use a cut-up straw w/a drill to mix. It's SO much better. And faster.
  4. BE SURE TO CLAMP THE MOLD AT THE TWO MIDDLE POINTS ON TOP!

AAAARRRRGGGHHHHH. The EPU Sticks to the polyethylene.

Try Number 3: new mold technique

Garbage bags work great. Make metal mold, cover with garbage bags.

Update 2003/11/10: EPU didn't work since it expands too much after it dries. We've since moved to 1/16 inch double-sticky polyethylene foam tape.