In this paper, two G-band sub-harmonic mixers based on planar antiparallel Schottky diodes are presented. The proposed type-I mixer is designed using the conversional THz Schottky diode mixer circuit architecture. In order to broaden the bandwidth further, a novel type-II sub-harmonic mixer based on new circuit topology is proposed. In type-II mixer, an antiparallel Schottky diodes chip is directly connected with metal ground using silver epoxy. The simulated results show that single-sideband (SSB) conversion loss of type-II mixer is less than 10 dB in the frequency range of 160-194.8 GHz. For validation, the type-I mixer is fabricated and tested. Measurement results show that single-sideband conversion loss of type-I mixer is basically less than 10.7 dB in the frequency range of 166-190 GHz.
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