To realize remote sensing at sub-millimeter wavelengths, a 450GHz sub-harmonic mixer was studied. An anti-parallel pair of Schottky diodes is the key component in the mixer. The length of the diodes is 74μm, and the cut-off frequency of diodes is up to 8THz. The suspended microstrip matching circuit was built on quartz, and the metal block was cut into two halves. The diode embedding impedance was calculated. The diode package and the matching circuit were integrated in the mixer model. The predicted single side band(SSB) conversion loss is 8.0dB, with 4mW of local oscillator power. Measured results indicate that the lowest measured SSB conversion loss is 14.0dB, with 5mW of local oscillator power. The loss is below 17.0dB in the band from 433~451GHz, with a 3dB bandwidth of 18GHz.