Power handling capability of microstrip and stripline?

Hello,

I need advice for two projects. I'm new to designing high power RF circuits.

I'm designing a directional coupler in stripline at f0= 638 MHz. The input port will be handling 300 W. The PCB board used will be RO4003C. I've used the Rogers Impedance Calculator on their website and am getting high temperature increases(40 C +) from ambient temp at that input power range. Is there something I'm missing in my design or is regular stripline not designed for high power like this?
I'm also designing an LPF in microstrip operating at 600 W. Same question applies as well. Am I better off using something else or can I negate the temperature rises with heatsinks placed on the ground planes for both designs?

Thanks

I think that's impossible.
you should use ALUMINA substrate.
AND BE CAREFUL ABOUT VSWR.
is the 300W pulse wave or CW?

I'll look into the alumina substrate. The coupler is for a transmitter's output but I'm not sure about the characteristics of the wave.

to choose the trace width capable of handling Power P=RI^2 you can use the following link:

http://www.desmith.net/NMdS/Electronics/TraceWidth.html

could you tell more about your coupler? is it using only two layers of RO4003? I think it is not possible to design 300W stripline coupler with two layers, beacause the line width will be very thin and cannot handle 300W.