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This paper presents a novel SiGe HBT sub-harmonic direct-conversion mixers for C-band wireless LAN application. The proposed down conversion mixer consists of single level I/Q-channel mixers and 90° phase shifters for each RF and LO input. Since the proposed sub-harmonic mixer requires only single ended RF and LO signal sources for generating I/Q base-band signals, the RF front-end can be greatly simplified compared to the fully differential RF front-end architecture from LNA and VCO to mixer. The measured conversion gain and input PldB are 13.6 dB and -15 dBm, respectively at 5.8 GHz RF signal and 2.9 GHz LO signal. I/Q mismatches caused by LO and RF 90° phase shifters and I/Q-channel mixers are less than 5° and 0.5 dB in phase and amplitude mismatches. Each I/Q-channel sub-harmonic mixer consumes 6.2 mA from a 2.7 V supply.