High frequency and power source is most important for terahtz technology, and multipliers is the best electronic way. This quadrupler design is only one stage to avoid impedance mismatches between multipliers. A proposed Schottky diode model improves the accuracy of design, which has considered the behaviors of current voltage (I/V), capacitance voltage (C/V), plasma resonance, and skin effect. Theoretical analysis was carried out by using harmonic balance simulations programs and three-dimensional finite element simulation tools to find the optimum embedding impedance for a given diode. Compact Suspended Microstrip Resonators (CSMRs) minimize the length/width ratio and make short idlers at the 2nd and 3rd harmonics. For experimental verification, the quadupler works at 325 GHz~351 GHz and output power is above 1mW between 334 GHz and 346 GHz, and the highest efficiency tested was above 3% with 100 mW.