A novel 21-35 GHz single-balanced quadruple subhar- monic monolithic passive mixer is fabricated using the 0.15 μm GaAs pHEMT process. This mixer consists of a local oscillation (LO) spiral balun and a radio frequency (RF) band pass filter which has an inter- mediate frequency (IF) extracted feature utilizing a pair of anti-parallel Schottky barrier diode to achieve quadruple subharmonic mixing mech- anism. The RF band pass filter formed with an interdigital coupler and a low-pass network is used to reduce the chip dimension while oper- ating at a low frequency band and to improve the isolation between the RF and IF ports with a broadband operation. From the measured results, the mixer exhibits 11.3-15.1 dB conversion loss, 28.8 dB-high RF-to-IF isolation, 40 dB-high LO-to-RF isolation, 60 dB-high 3LO- to-RF isolation over a 21-35 GHz RF bandwidth, and an input 1 dB compression power of 4 dBm. The compact IF extraction circuit sup- ports an IF frequency ranging from DC to 3.1 GHz. The core chip size is only 0.67 × 0.75mm2.
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