[Moon-net] Arc-overs in a PCB on 2320MHz

[Koellner, Guenter]

Hello,
 
maybe some of you can give me some advise...
 
On 13cm, I am running two of the well known Ericsson (or was it Nokia?) modules. You can see those on this web page:
http://sk0ct.se/2g3pa/2g3pa.htm
My coupler is different, but professionally made and working fine.
 
My problem is that at the output of the modle, about where you can see the semi regid connected in the pictures, I am getting arcs through the PCB to the ground plane caused by excessive RF field. While transmitting, you can really see them, and I even saw the solder melting there. The PCB is 0.65mm thick and the stripline 4mm wide. Due to these arcs, the PCB becomes carbonized, which is afterwards like a ground short at that point. Luckily the MRF21120 are safe against the worse return loss, so I never damaged one due to this.
The total output power is about 200W, so I assume having a little more than 100W on each module. I am operating the units in a rain-dry cupboard behind my dish, so environmental conditions are "outside" ones.
 
When this happend first, I cut away the carbonized piece (about 3mm wide x 5mm long) of the module's PCB and replaced it by a piece of insulation and a copper foil. But meanwhile another arc over happend at the inner end of my cutaway, and the 2nd module had an arcover at its originally kept output, too.
 
I already thought about replacing the stripline with semi rigid. I roughly calculated the impedance to be about 20Ohms due to the mechanical dimensionsions. So I probably can use two 50Ohm SR in parallel if these can withstand the power much better.
 
I also had a talk with the developer of the UMTS amps in my company, he also mentioned that they know about such problems.
 
What would you do in my case? Is it a good solution to replace the stripline with two 50Ohm semi rigid lines in parallel or any other hints?
 
73, Günter, DL4MEA