Abstract: According to the three-dimensional structure featuring variety of materials around an anti-parallel pair of planar Schottky diodes barrier, the 3D-circuit around the diode barrier can be calculated as a four-port diode modal S-parameter package, and the S-parameters produced by the electromagnetic field solver connecting to the non-linear model of the Schottky diode barrier were incorporated into the non-linear circuit simulator as the diode's whole model, and by this way the whole monolithic mixing circuit's behavior could be modeled more accurately. The monolithically integrated 330 GHz sub-harmonic mixing circuit was fabricated on a 12m thick GaAs membrane, and it was suspended in a LO and RF reduced height waveguide split block. The MMIC demonstrated performance with a best double-sideband-mixer conversion loss of 10 dB with 5 mW of LO incident power at 330 GHz. It could withstand some mechanic pressure when its outer environment temperature change, because it was mounted via four flexible beam-leads and a fixed end in a waveguide block.