In this paper, we study the feasibility of using CMOS circuit blocks for designing future light weight, small in size atmospheric remote sensing receivers. A compact CMOS down-converter is designed which operates from 160 to 188 GHz and includes a sub-harmonically pumped I/Q resistive mixer, two IF amplifiers and a voltage controlled oscillator (VCO) with LO buffer. A measured down-conversion gain of +2.6 dB is achieved with a total dc power consumption of 152 mW using the nominal supply of +1.2 V. The measurement results show a 3 dB IF bandwidth from 1 to 5 GHz and the VCO tuning range is from 85 to 89 GHz. The designed CMOS MMIC down-converter including the probing pads occupies a silicon area of 0.575 mm².