The development of a 220 GHz frequency doubler based on GaAs plannar Schottky diodes is described. The doubler works at room temperature, and its structure is very simple. A plannar Schottky varactor flip chip with four anodes arranged in anti-series is mounted onto a quartz based microstrip circuit to realize frequency multiplication. DC bias is put on the varactor through a low-pass filter circuit which is also constructed on a quartz microstrip. All the quartz circuits are glued into the waveguide block with conductive adhesive. The block is split in the E-plane and its surface is gold plated. Test data for the 220 GHz doubler show 15 mW output power with 5% efficiency when appropriate external bias resistor is selected. Over the 213-230 GHz，the output power of the doubler is above 10 mW，and the power fluctuation in this band is very small.