A 24–44 GHz Broadband Subharmonic Mixer With Novel Isolation-Enhanced Circuit

A 24 to 44 GHz upconversion broadband subharmonic mixer with a novel isolation-enhanced architecture is presented through a 0.15 μm GaAs pHEMT process. Total chip size including probe pads is less than 1.33 × 0.82 mm
²
. The isolation-enhanced circuit is constructed from two directional couple lines both formed with three microstrip lines. They are used to enhance the isolation between IF/LO-to-RF and LO-to-IF. IF and RF pre-amplifiers are employed to achieve high conversion gain for subharmonic mixing of anti-parallel diode pairs. Based on the unilateral characteristics of an IF pre-amplifier, the LO/RF-to-IF isolations exhibit substantial improvement. From the measured results, the conversion gain of the mixer is 6.0 to 10.5 dB operating at RF frequency of 24 to 44 GHz. The IF-to-RF, LO-to-IF, LO-to-RF, and 2LO-to-RF isolations are 24.5 to 27.1 dB, 32.4 to 39.6 dB, 20.6 to 24.6 dB, and 48.4 to 65 dB, respectively.