A novel GaAs monolithic integrated DC-coupled up-converter is presented. It up-converts a 0.1- to 0.5-GHz signal to 0.6 to 1.75 GHz. The high level of integration has been achieved in a small chip size of 1.22 mm × 1.22 mm by utilizing active matching techniques. A wideband local oscillator (LO) amplifier, an active 180° splitter, a double-balanced mixer, an RF amplifier, an actively matched IF amplifier, and an RF blanking circuit are integrated on a GaAs chip. The up-converter exhibits an 8-dB conversion gain, a maximum input/output voltage standing wave ratio (VSWR) of less than 1.6, and a 40-dB RF blanking for an IF of 0.1 to 0.5 GHz and LO of 0.5-1.25 GHz. The measured results are in good agreement with the simulated results.