ADS question

I've designed band-pass filter in ADS (operating in 3GHz about) using capacitors and inductors, but how can I convert the design to microstrip lines filter?

You can consider "the inductances" as short circuited microstrip lines and also you should imagine "the capacitors" as open circuited microstrip lines.Therefore, you will obtain a set of microstrip lines and then place them on your substrate.
But this method won't give the exact response of your designed filter due to coupling effect of your lines, so this won't be the same filter.
Instead of it, why don't you use a filetr design progam such as Genesys tools to design and optimize ? Or you can use in ADS filter design guide which is quite proper for your purpose..

If you what to try and translate L's & C's to Microstrip line you can try this method.
(See attached File)

But I would use a filter design guide or just look up the type of filter you are
using ( 7 Poll Butterworth ...) online and if you find a printed filter you can
just use the general shape just rescale it to your frequency, εr, Thickness
and the just you the "Tune" option in @DS the put it into momentum to see
if the S-Par sim and the Momentum sim are close. Usualy thier not , but for
printed circuits I would go with Momentum. Unless you have Eagle Ware.

Cheer

What I'm trying to do is to transfer my filter into coupled lined microstrip filter (I think this is the correct name in english). I have to use only ADS (this is what we have at place where I study).Is there a way to directly convert it, or do I have to design it from the begining?

No, you can definitely use your prototype !

Get a hand on "Microwave Engineering" by David M. Pozar, I think its popular enough so there is a good chance you have it in your college's library,

Go to Ch. 8.7 p.474-p.485,
Its a specific recipe for converting your lumped prototype into coupled lines BPF.

Good luck,
P.

you can use smith chart and calculate the corresponding length and width of microstrips.

in ads it have a tool that can convert between lump and distribut.

How exactly can I do it? I've searched it and didn't find
Can ADS automatically transfer my filter to microstrip coupled line filter?

How exactly can I do it? I've searched it and didn't find
Can @DS automatically transfer my filter to microstrip coupled line filter?