Wideband downconversion mixers are demonstrated by using both 0.35‐μm SiGe heterojunction bipolar transistor (HBT) and 2‐μm GaInP/GaAs HBT technologies. 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 article 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° hybrids to cover more than 8:1 bandwidth. The SiGe HBT Micromixer achieves the conversion gain of 6 dB, IP1dB of −17.5 dBm, and IIP3 of −7 dBm with the 3.3‐V supply voltage and the power consumption of 37.5 mW. On the other hand, the GaInP/GaAs HBT Micromixer achieves the conversion gain of 25 dB, IP1dB of −25 dBm, and IIP3 of −15 dBm with the 5‐V supply voltage and the power consumption of 50 mW. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2254–2257, 2008; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.23642