Hi,
Unfortunately I have not built IQ mixers for the GHz band so no experience.
But some info on the internet may be of some help to see how others do it:
maybe one of the Linear Technology IC product at h**p//www.linear.com/prod/datasheet.html?datasheet=826 (replace * with t)
or the Remec page at h**p://www.remecmagnum.com/Components/Mixers/IQMixers.html
Also if you search with google.com for words like IQ mixer, you will receive several hits of interest to this topic.
regards, unkarc