A wideband downconversion mixer is demonstrated using 0.35-μm SiGe heterojunction bipolar transistor (HBT) technology. A micromixer topology is implemented in the RF port while a differential type shunt-shunt feedback amplifier and a differential-to-single CE-CC output buffer are used in the IF stage. The frequency response analysis and systematic measurement approach for a wideband Gilbert mixer are proposed in this paper for each individual stage of local frequency (LO), radio frequency (RF), and intermediate frequency (IF). The differential LO signals are generated by several off-chip 180 degree hybrids to cover more than 8:1 bandwidth. The downconversion Gilbert mixer achieves the conversion gain of 6 dB, IP1db of -17.5 dBm, and IIP3 of-7 dBm. The power consumption is 37.5 mW at 3.3V supply voltage.