wideband directional coupler 100w

I want to design and build a high power, up to 100W wideband 20MHz - 500MHz directional coupler with 30dB - 40dB coupling

Any suggestions?

Thanks in advance

You are looking for a stepped directional coupler. The unit will be large though !.

Paul.

I am also interest in issue
How to build bi-directional coupler 800MHz÷2200GHz?

Look at this paper. The same design idea with high power coax cable is introduce in old russian papers at http://cityradio.narod.ru/tuning/napr_otv.html