I'm currently working on a coherent detector for radar. It uses I/Q downconversion and I'm trying to find any possible help on techniques, principles, schematics, common problems with I/Q designs. Any help is appreciated.
I think I know of a good book to suggest you that most likely have all the answers to your questions. Take a look at the book: "Communication systems", Simon Haykin, John Wiley & Sons, 1993, 3rd edition.