PCB TRACE - handling 1500W

[majorbra]

Hello!!

Im my power combiner design, i need to pass 1500W CW(110Mhz) in a microstrip.

My microstrip details are: Impedance: 74 ohms, trace width: 130mils, condutor Thickness: 2OZ, distance between the ground plane and conductor:120mils, tanD:0.0018, Er:3.5

The laminate is a TACONIC RF35.

In your opinion, can this trace size handling this power reliability?

Tks all.

 

[cks3976]

You can refer these previous threads with similar question...

https://www.edaboard.com/threads/158072/
https://www.edaboard.com/threads/182028/

And this calculator might be of use : The CircuitCalculator.com Blog » PCB Trace Width Calculator

 

[majorbra]

Tks cks3976 but, if possible, I would like to get an analysis in terms of RF power.

Regards.

 

[biff44]

It might get a tad warm. A quick (not rigorous) back of the napkin calculation says:

Loss tangent is 0.0018. assuming 2" long line at 2.4 GHz, that is a loss of 0.05 dB sent directly to heat. For 1500W that would be 1.5 watts of heat per 2" of line.

rf35 has k=0.24W/m/K thermal conductivity.

Thermal resistance is R = X / kA

Assuming the heat flow directly down from a 120 x 2000 mil trace, with a 130 mil thick dielectric, converting that to meters gets you a thermal resistance of R=89 deg C/Watt

So your top trace will get to T = R * Power = 89 degC/watt * 1.5 watts = 133 deg C above the baseplate temperature. That is pretty warm!

I did some fast analysis, but it looks like ~2/3 of the loss is in the dielectric, so either find a lower loss one, or one with a higher thermal conductivity.

(and, of course, you have to worry about voltage arcing too at the connectors!)
Rich


p.s. you should check my math for mistakes!

 

[majorbra]

Biff, just a note: the trace width: 130mils, and the thick dielectric=120mils.

regards.

 

[biff44]

Easy for you to recalculate. Check out these two materials: RO4350B™ and RT/duroid® 6035HTC

 

[shush]

I am designing a filter on PCB that should stand for 200wt@2170 MHz,
the s21 as it seen on the VNA is around -0.4dB, does it mean that around 17wt is going to stay on the traces and convert to heat?
i made it with wide traces in order to have better heat flow and used 1.6mm substrate, how do i calculate the delta T that going to be, except of frying it with real amplifier.
i made my pcb was from neltek9250 which had 0.25 thermal conductivity but great tan delta, and i made another one for 3.5 epsilon in case of a use of rogers material.
how can i predict the heat on the pcb and what is the right way to connect the ground to a heat sink(silicon pad etc.)
the pcb dimensions are 200x55 mm.
i have seen in all kind of solid state transistors for 58dBm amplifiers assemblies a rogers 4350 material were used with thin trace.
tnx