A 220-GHz Balanced Frequency Tripler With Independently Biased Schottky Diodes

A 220-GHz balanced frequency tripler with independently biased diodes is presented. By introducing parallel coupled suspended lines in the circuit, an even mode signal is supported to propagate and excite the diode pair involved in the tripler in antiphase, thus the even harmonics are suppressed. By using two physically separated suspended lines, the diodes can be biased with different voltages and the circuit imbalance can be compensated. The presented tripler does not require any ON-chip capacitor or discrete bias-tee, thus the circuit size and requirements on the circuit fabrication technology are greatly reduced. A prototype using a discrete diode and quartz substrate is fabricated, assembled, and measured. Measurement shows with 160–220-mW input power, a typical efficiency of 8% can be achieved, the average output power is 17 mW, and the 3-dB bandwidth covers the 212–228-GHz band. The output power can be improved by about 6.5% with an independent bias for each diode chip.