A 54-66 GHz sub-harmonic monolithic passive mixer using the standard 0.15 μm pHEMT process is demonstrated. The proposed mixer is composed of a hairpin diplexer, an open stub, and a low-pass filter. The mixer also utilizes a pair of anti-parallel diodes to achieve a subharmonic mixing mechanism. The hairpin diplexer formed with two parallel-coupled line band-pass filters is used to improve the isolation between the radio frequency (RF) and local oscillation (LO) ports. The low-pass filter supports an intermediate frequency (IF) ranging from dc to 1 GHz. This proposed configuration leads to a die size of less than 1.5 mm2. With a conversion loss of 15.2--18.3 dB, the 2LO-to-RF isolation is found to be better than 27.5 dB. A high LO-to-RF isolation of 23.5--45 dB over 54--66 GHz RF bandwidth, as well as 1 dB compression power of 8 dBm, can be achieved.
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