A novel planar dual balun for Doubly Balanced star mixer

A novel planar dual balun for doubly balanced star mixer is presented. The balun consists of two identical Marchand baluns using coupled microstrip lines. It shows the amplitude imbalance within 1.2 dB and the phase imbalance within 180/spl plusmn/1.5/spl deg/ over 1.2 to 2.8 GHz. The star mixer using a pair of the suggested balun has the conversion loss about 6 dB in the band.