An accurate design approach of full WR-3 waveguide band balanced frequency tripler is proposed in this paper. Compact Suspended Microstrip Resonator Cell (CSMRC) is adopted for input filtering and circuit matching. CSMRC brings relatively higher out-of-band rejection and reduce the size and the channel width of the tripler. The entire tripler is composed of two waveguide-to-suspended stripline transitions, a pair of two anti-parallel diodes, a CSMRC and two matching lines. The design approach is verified by comparing the measured results with the simulated ones. The measured output power of two samples is between 45 to 95 μW at frequencies from 225 to 330 GHz, and the average output power is 60 μW. The conversion efficiency is from 1.5% to 3%, and the optimum efficiency is 3% with +5 dBm drive power.