The frequency conversion function of a mixer plays a critical role in RF and microwave systems in determining their overall performance. For example, the quality of data transmission in the wireless communication systems and the identification of targets using radar and sensor systems are entirely dependent on the mixer performance in the receiver systems. The microwave/millimeter‐wave systems that operate at a number of frequency bands are susceptible to intermodulation frequency products generated in mixers. Spurious signals or distortion in mixers continues to be a problem in virtually all the RF and microwave systems. Therefore, mixers are frequently the dominant components in the receiver in establishing the system's distortion free performance. As a result, microwave and millimeter‐wave mixers have been the subject of continuous research and development for the past several decades and will continue to be the subject of future research in order to make the systems more efficient.