Vector modulators (VM) and phase shifters are essential components in phased array antennas with electronic beam steering. This work presents an IQ reflection-type vector modulator using PIN diodes, designed and implemented to operate at 28 GHz. An extensive characterization was carried out, especially concerning bandwidth and input/output return losses. This modulator is capable of producing a 360° phase shifting with a minimum attenuation of 14 dB at 28 GHz, and has a measured bandwidth of 3.6 GHz. A digital control system for the vector modulator was also developed, allowing to obtain pre-selected constellations points, with a measured 0.4 dB of maximum absolute error in amplitude and 2.6° in phase. Additionally, the designed VM was employed in a practical application, where analog beamforming is implemented in a 4×4 transmitter phased array allowing to perform a complete electronic control of the radiation pattern of the array.