Passive broadband millimetre-wave uniplanar MMIC balun

A new uniplanar monolithic microwave integrated circuit (MMIC) balun using lumped circuits is presented. The proposed planar balun consists of a wideband Wilkinson power divider and a broadband 180deg phase shifter using novel series and parallel LC reflective terminating circuits. To demonstrate the design methodology, a 24-44 GHz MMIC balun was realised as a 1.4 mm GaAs chip. The measured return losses for the unbalanced and balanced ports are better than -12, -10 and -7 dB, respectively. The measured amplitude and phase imbalance between the two output ports are less than 0.5 dB and 7deg, respectively, and maximum insertion loss is 5 dB.