Räisänen was appointed to the Professor Chair of Radio Engineering at TKK in 1989, after holding the same position in 1985 and 1987–1989.
He has held visiting scientist and professor positions at the Five College Radio Astronomy Observatory (FCRAO) and University of Massachusetts Amherst (UMass), Amherst (1978–1981), at Chalmers University of Technology, Göteborg, Sweden (1983), at the Dept.
Räisänen is supervising research in millimeter-wave components, antennas, receivers, microwave measurements, etc.
He has authored and co-authored more than 400 scientific or technical papers and six books, for instance, "Radio Engineering for Wireless Communication and Sensor Applications".
He served as an Associate Editor of the IEEE Transactions on Microwave Theory and Techniques from 2002 o 2005.