A Q-band monolithic AlGaAs/GaAs HEMT CPW downconverter

A fully-integrated HEMT (high electron mobility transistor) MMIC (millimeter-wave IC) downconverter is designed and fabricated using coplanar waveguide (CPW) structure. The CPW design is a high-yield approach because it simplifies the MMIC process by eliminating the yield-limiting backside process. The downconverter circuit consists of a two-stage RF amplifier, a singly balanced HEMT gate diode mixer, and a two-stage IF amplifier. The downconverter receives Q-band RF frequency and downconverts it to a 2-4 GHz IF frequency. The measured conversion gain is 8 to 11 dB. The LO (local oscillator) to IF isolation is better than 30 dB. The chip size is 1.4 *4.0 mm/sup 2/.<
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