can FR-4 handle 25o watts?

can fr-4 material handle 250 watts of power ? what dimensions would be needed ? urgent help needed plz

The Key is temprature.Not Power. Fr-4 can work at most 200oC.I think.

At FR4, for 200W, the Amp is sqrt(200W/50R)=2A. I think 50R line of FR4 should be at least 3mm width to stand the 2A. If you use 1mm width line to stand 2A, the system MTTF should be very short.
What is your frequency?
Normally the tan(delta) of FR4<=0.035, so you can simulate in Microwave Office to find the microstrip loss is how much dB/m. Then you can calculate how much loss of power on FR4 from 200W.
And RO4350B Er temperature cofficient is 50ppm/deg, you can find that FR4 is worse than RO4350B. At 0deg~70deg temperature, the Er of FR4 can vary about 20%. So notice that.

Seriously, the question can't be answered without knowing a frequency.

Exactly. Frequency, board thickness, cuttouts in the board for components, how you plan to get the heat out of the back of the board, cover proximity, connector attachment, operating altitude....a serious lack of info provided.

i have to design an antenna with frequency from 1 to 3 ghz

There's a number of right answers above (temperature, etc). If the antenna dissipates 250w of heat would also be one of my concerns. That's a lot of smoke. Pulsed or Continuous Wave?

Your biggest problem will be the dielectric loss producing heat. I have seen 600 W HF amplifiers made on FR4 with no problems. What you might do is have several lower power amplifiers with coax output and then have a separate combining module possibly using more suitable microwave substrate. This would give you a sort of cost compromise.

Hello,

Now it becomes even more difficult to answer, what type of antenna do you have in mind? If you make a multi resonator patch antenna, both E-field and electric currents increase due to resonance (hence heat loss). If it will be more or less a travelling wave structure (without ground plane under it), field and current will not increase that much (or reduces).

I assume you have access to antenna modeling SW. So you can check radiation efficiency to see how much power is radiated (and the rest is converted to heat). If you can accept low impedance lines, both dielectric and ohmic losses/surface area decrease (wider traces, less voltag/E-field).