A D-band frequency doubler with quartz substrate is proposed in this paper with commercial planar Schottky diodes DBES105a. The balun in the doubler is implemented by finline-suspended-stripline coupler (FSSC). The waveguide-to-finline transition suit for quartz substrate has only 0.15 dB measured insertion loss. Compared with traditional coupler in balanced doubler and mixer designs, it has the advantage of easier bias for the diodes. Measured results of the doubler showed that the maximum output power is 3.39 mW with 0.4 V reverse bias voltage and 26.3 mW drive power. Its corresponding peak efficiency is 12.9%. The output power of the doubler is reduced from 3.1 mW to 2.0 mW when the bias voltage deviates from its optimum bias condition. The finding shows that proper external DC bias for Schottky varistor multiplier is as important as for schottky varactor diode frequency multiplier.