Abstract: In this paper, the design and performance of a U-band integrated finline-suspended stripline mixers aredescribed. The mixers use Schottky-barrier diodes MA4E2037 of M/A-COM. The substrate material is RT-Duroid 5880 withthe thickness of 0.127 mm. The RF port uses the finline structure and the LO port uses the waveguide-microstrip probestructure. Finally the signal uses the SMA connector. For the structure, the conversion loss of less than 8.71 dB and the LO/RF isolation of greater than 25 dB have been achieved with the LO at 42 GHz and the RF swept from 40 to 60 GHz.