The quadrature modulator is a crucial block in transmitters that upconverts baseband signals to the Radio Frequency (RF) band of interest using local oscillator frequencies. In this paper, non-ideal factors that influence the performance of the quadrature modulator are considered, and solutions are accordingly taken in the quadrature modulator design. A high-linear RF quadrature modulator with improved sideband suppression and carrier leakage performance is presented in this work. The quadrature modulator implemented in the 0.18-μm SiGe process uses the current bleeding technique to improve the general performance of the double-balanced active Gilbert mixers. An on-chip prescaler followed by two cascaded limiting amplifiers is designed to provide accurate quadrature local oscillator signals. Predrivers at quadrature baseband signal input ports are proposed to eliminate DC offsets. The measured sideband suppression achieves a performance of better than −43 dBc and carrier leakage is less than −38 dBm over the output RF frequency range of 30 MHz to 2.15 GHz. The output 1 dB compression point equals 11.4 dBm at 800 MHz.