Direct modulation at microwave frequencies promises the advantages of compact size, low cost, and relatively simple system design. In this paper, a novel architecture of a direct-vector C-band modulator is described. In particular, a subharmonic mixer is used to overcome the high carrier leakage that is associated with conventional fundamental modulators at microwave frequencies. The topology exhibits relative low conversion loss (11 dBc) and good image frequency rejection (23.5 dBc) and local oscillator (LO) rejection (23.9 dBc). The LO power level used by the mixer is approximately 6 dBm for optimal performance in the operating band.