Abstract: A broadband miniature doubly balanced diode mixer chip fabricated by Win’s 0.15 μm pHEMT technology is presented. In order to save chip area, a four-fold modified Marchand balun is used. A coupled line U section improves the port to port isolation and provides the IF-output port. The mixer achieves a low conversion loss of 5.5 to 10.7 dB and high isolation of more than 26 dB over a 26–40 GHz RF/LO bandwidth and a DC–14 GHz IF bandwidth. The mixer’s chip size is around 0.96 mm2.

Key words: doubly balanced,  Marchand balun,  conversion loss