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A wideband 77-GHz front-end receiver for passive imaging has been designed and characterized. This system comprises a fully differential low-noise amplifier (LNA), double-balanced mixer, and voltage-controlled oscillator (VCO). The 77-GHz LNA achieves 4.9-6.0-dB noise figure (NF), 18-26-dB gain, and S11 and S22 of - 13.0 and - 12.8 dB, respectively. The double-balanced mixer achieves 12-14-dB NF, 20-26-dB conversion gain, and -26-dBm P1dB (input referred). The VCO achieves output power from - 2 to 0 dBm with phase noise of ~ -93 dBc/Hz at 72 GHz, and can be tuned by approximately 3 GHz. The NF can be substantially improved with the addition of image-reject Chebyshev bandpass filters at the interface between the LNA and mixer. The 77-GHz receiver achieves 40-46-dB max conversion gain, output-referred P1dB of 2 dBm, and power dissipation of 195 mW. A 90-GHz LNA has also been characterized as an integral part of a higher resolution 94-GHz imager. This LNA achieves 22-dB maximum gain, 7.0-dB NF, and - 25- and - 10-dB S11 and S22 , respectively, at 90 GHz. This LNA also exhibits excellent ultra-wideband performance, achieving ges 10-dB gain from 40 to 100 GHz.