circuit isolation using optocoupler

I am looking for a very high isolation between two microwave circuits(4GHz)(isolation > 50dB).
Is it possible to use a optocoupler between these two circuits?
What should be the specs and type of optocoupler, i should use?

Kindly help by sending some details on such a application.

thanks

What do you mean by "isolation between two microwave circuits"?

Are you looking for a device that passes the signal in one direction only? These devices are available, based on ferrite materials -> "isolator"
http://www.novamicro.com/drop-in-isolators

isolation normally means reverse isolation,i.e signal passes unattenuated in forward direction and gets highly attenuated
in reverse isolation.
Ferrite isolators provide isolation < 20dB, in above case you need 3 isolators in series, which is not a good design.

yep, you can easily get 90 dB of isolation if the light source and the detector are under different metal shields, with F/O cable running between them.

If you try to do it all on one PCB, you will probably only end up with 50 to 60 dB of isolation.

Using a single optocoupler...you issue will be isolating the ground currents from the input to the output halves of the circuit, as well as upper frequency response limits of a simple low frequency optocoupler.

thanks biff44, this is what i am looking for. My application is PCB based,Can you please suggest a link or application note,from where
I may get some more details on this.

BUT hang on .... you cant use opto couplers as isolation in a RF transmission path
you have to use circulators or something similar


Dave

Even in one PCB, you can also split the GND into two part. So get greater isolation.50dB is not so much, I guess shielding can can do so.