This work studies a concept for a 90° vector-sum phase shifter operating at 54.6GHz, which delivers a high output power over a wide bandwidth of 20GHz, corresponding to a relative bandwidth of 37.2%. The circuit was designed to control the phase in a local-oscillator chain and was realized in a 130nm SiGe BiCMOS technology. A root mean square (RMS) magnitude error of only 0.23dB is paired with an RMS phase error of 0.89dB, achieving linear control with only one un-calibrated analog voltage. An output-referred 1dB-compression point oP 1dB of 5.0dBm is achieved at 60GHz with 11.3dB gain and a power-added efficiency of 6.3%. The high output power qualifies this circuit to directly drive state-of-the-art frequency multipliers and leverage their multiplication factor to reach mm-wave bands with 360° of available phase control. To the best knowledge of the authors, this circuit demonstrates the highest output power and power-added efficiency reported for phase shifters operating at about 60GHz or above, while still providing high power gain.