Concurrent dual-band switch-mode power amplifiers require high common-mode impedance at their intermodulation frequencies. Baluns utilizing quarter-wave effects only have perfect open common-mode impedance at their design frequency. Attempting to use a balun without taking the new dual-band requirements for common-mode impedance into account will result in efficiency loss. However, the addition of some transmission lines can add impedance at those specific frequencies by rotation of the common-mode impedance without affecting the differential mode match.