Wideband Fourth-Harmonic Mixer Operated at 325–500 GHz

This letter presents an approach to design the fourth-harmonic mixer based on a pair of antiparallel Schottky diodes. To implement the proposed fourth-harmonic mixer, a two-level local oscillator (LO) low-pass filter is used to suppress the second, third, and fourth harmonics of the LO frequency, further to improve the isolation between RF and LO ports. Also, two shorted grounds are adopted to ensure the wideband performance of the proposed mixer. Furthermore, a wideband fourth-harmonic operating at 325–500 GHz is fabricated and measured. The results show that it has very low conversion loss from 15 to 22 dB in the whole operational band.