An up-conversion mixer includes a first and a second hybrid couplers and a first and a second traveling-wave mixers is disclosed. The first hybrid coupler receives an input intermediate frequency (IF) signal and produces a first IF signal (IF1) and a second IF (IF2) signal, the second IF signal being 180 degree off-phase compared to the first IF signal. The first traveling-wave mixer mixes the first IF signal (IF1) and a first local oscillator (LO1) signal to produces a first radio frequency signal (RF1). The second traveling-wave mixer mixes the second IF signal (IF2) and a second local oscillator signal (LO2) to produces a second RF signal (RF2). The second hybrid coupler to combines the first RF signal and the second RF signal to produce an output RF signal. The use of the traveling-wave mixers allow for a wide bandwidth operation of the up-conversion mixer.