In this letter, a 120-220 GHz fourth-harmonic mixer based on Schottky diodes is presented. To broaden the bandwidth, a novel diplexer is proposed, which consists of two low-pass filters (LPFs) and a beam lead capacitor. Thanks to the high-pass characteristic of capacitor, the 30-55 GHz local oscillator (LO) signal is efficiently pumped to the diodes. Moreover, a two-level hammer-head configuration is adopted at the LO LPF to block the 120-220 GHz radio frequency (RF) signal. Finally, a 120-220 GHz fourth-harmonic mixer is fabricated and measured. The measurement results show that the conversion loss ranges from 12 to 18 dB within a wide RF relative bandwidth of 58.8%.
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