180 Hybrid Coupler at 20Ghz

Hey guys
I am designing a 180 hybrid (rat race) on 20Ghz. My choices are microstrip or CPW. Any ideas on what i should choose? Also any idea a about the effects on different dielectric thickneses? Any prior experience or references are welcom. Thank you in advance.
George

At 20GHz, for a rat race coupler you can use any low-k substrate. The FR-4 Teflon substrate is good and low-loss.
Substrate thickness is not too important; the active lines width depends on it, this is all.

20GHz use FR4? the problem is FR4's Er is not consistence.

If you think so... I have not tested FR-4 for such inconsistence, but I have used 20-mil 50-Ohm strips at over 90 GHz without problems. I have not tried to make a rat race on it.

What do you mean by FR4 Teflon substrate?
FR4 uses high loss dielectrics, whereas teflon substrates are low loss. Very different materials.

You are right, I misfired ! For a long time I used Rogers substrates put in a box labeled FR-4.
Sorry, i must correct my box labels as well as my wrong advice.