A Q-band miniaturized uniplanar MMIC HEMT mixer

A miniaturized uniplanar GaAs MMIC HEMT mixer is proposed based on a compact multifunction transition structure. By the independence nature of the coplanar-waveguide (CPW) mode and the coplanar-stripline (CPS) mode, a compact transition which converts the CPW mode into the CPS mode is realized. This transition structure also has the functions of 180° hybrid, RF and LO diplexer, and bandpass filter. Thus the size of the proposed mixer may be drastically reduced, and the LO-to-IF and LO-to-RF isolations and RF conversion gain are excellent. This mixer is designed to operate with RF frequency from 35 to 40 GHz, IF frequency from 0.5 to 6 GHz, and LO frequency at 35 GHz. The lower sideband conversion gain is about 5 dB, the single-sideband (SSB) noise figure is 6.5 dB, the isolations are all better than 30 dB, and the size of the mixer is much compact than those of the conventional mixers.