Hi Stéphane,

Just so you don't confuse people you talk with, "stripline" is a line
sandwiched between two ground planes (could be air dielectric or
circuit board dielectric), but if it's a PC board with ground plane on
one side and a trace on the other, that's "microstrip."

I think 1.6mm thick fiberglass epoxy, with a 50 ohm microstrip line on
it at about 3mm line width, will handle 100 W at 450MHz just fine.

You can make a stripline or microstrip coupler that's shorter than 1/4
wave, and it should still have good directionality. It just won't
have as much coupling as it does at 1/4 wave. The coupling at 1/4,
3/4, 5/4, etc., is all the same, and there are nulls at DC, 1/2 wave,
2/2, 3/3, etc. The maxima are rather broad, rounded, and not sharp
peaks. I think I found a plot of the response on the web recently,
but perhaps I made it from formulas.

If you don't get it somewhere else, I can scan and send the ARRL
article on making an SWR meter using copper pipe fittings. I suppose
they are US-standard fittings, but there should be reasonable
equivalents in the civilized metric world.

Cheers,
Tom


"Stéphane Rey" wrote in message ...
Hey Tom,

Thanks a lot, I'm going to download this software and have a look. My mind
was the power should be limited very low with PCB striplines, and I would
like to design something up to about 100W.

Stephane

"Tom Bruhns" wrote in message
m...
I'm not sure what's in current versions of the ARRL VHF/UHF manual,
but I know that older ones have articles on building SWR bridges. You
can just delete the detectors if you want to use them as directional
couplers. Also, you can download "RFSim99" for free, and you will
find in it a little design ap for directional couplers, in microstrip,
stripline, transformer-type, lumped and transmission line. The ap is
under "tools--components--coupler" in the pulldown menus. Note that
the microstrip and stripline assume the coupler is 1/4 wave long for
the given coupling--something the ap fails to point out.
Interestingly, 1/4 wave couplers (microstrip or stripline or the like)
give the same coupling at 3/4 wave...in other words, at the third
harmonic, which is useful for 146MHz and 440MHz. This is not true of
the lumped. The transformer style depends on the bandwidth of the
transformers.

Cheers,
Tom


"Stéphane Rey" wrote in message
...
Hello,

I'm looking for documentation explaning how to design and built
directional
couplers for 2m and 70 cm application.

I've found a lot of links for the theory but nothing explaning how to
compute the parameters and built it .

Any suggestion appreciated

Thanks
Stephane, F1TJJ