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This paper describes a low-noise subharmonic mixer MMIC for 76-GHz automotive radar systems. To improve a noise figure in a 100-kHz low IF band, a low 1/f-noise Schottky barrier diode (SBD) has been developed for the mixer. This SBD can offer 20 dB better 1/f-noise levels than a conventional HEMT type SBD can under the same operating current density condition. The fabricated mixer delivers a measured conversion gain of better than -9 dB and a measured noise figure of 12 dB under the condition of a 3-dBm low LO power and a 100-kHz low IF band. This noise figure is 26 dB lower than that of an HEMT type SBD subharmonic mixer with the same circuit topology. To our knowledge, the noise figure at the low IF band is the best performance of 76-GHz mixers ever reported.