What are qualifications needed by this Circuit Designer?

I would look for someone that has a Master's degree in electrical engineering ideally specializing in analog circuit design and/or RF circuit design, along with previous experience designing analog circuits.  Designing analog/RF circuits is quite complicated and typically takes years to master and that's after you finish school. When I was hired as an analog  IC circuit designer for Texas Instruments my new boss told me it takes most engineers 4-5 years before they can be really good analog circuit designers.  That was for integrated circuit design which has an even steeper learning curve, but in general good analog circuit design takes years to master.  So look for someone with at least several years of experience designing circuits.  The more circuits you design the better you get at it. Be  sure to check out my blog where I write about all aspects of  developing, prototyping, manufacturing, marketing and selling an electronic product. http://TeelEngineering.com/teblog

Your question is a bit vague, determining exactly what you want to do will get you to right candidate if you want to design a piece of electronics (a system) that communicates wirelessly and you're using chips that you can buy from a distributor (say digikey) then you don't need a circuit designer (circuit designer implies someone who can design circuits inside a chip) you will need a system designer/component engineer, someone who knows how to select the right chips and drive the PCB design and test to get you a working system if you want to design your own integrated circuit, 1st of all that's a much more expensive process, 2nd you will need a team of IC design (analog /mixed signal, digital), layout and CAD engineers