60W,1GHz RFload

Its quite simple really...

Just figure out what the maximum temperature of the resistor element in the load can be, then figure out the highest ambient temperature it will be used in and you have your temperature gradient at full load of 60 Watts.

Then just add together the thermal resistances at each thermal junction to find what power heatsink you need...

Let's assume perfect thermal connection between heatsink and resistor, if you have a maximum resistor temperature of 100 *C and a maximum ambient temperature of 40 *C, the maximum temperature gradient is 60*C/60W = 1 *C per watt.

So you just look for a heatsink big enough to have a 1*C per watt rating... Obviously it would be better to over-rate the heatsink so look for one that has a 0.5 *C per Watt rating...

John.

May be simply to get (buy) 100W resistor and forget about heatsink. Such resistor will work normal but be hot therefore don't touch it by hands.

One could try amateur radio equipment suppliers for off-the-shelf parts?

You can use pure resistive load and 60W is only a power of a small bulb so you may need only a small heat sink across the resistor. Look for these resistors for 60W termination using 50 Ohms impedance or whatever required by your RF source.