Broadband, planar, doubly balanced star mixers

Planar broadband star mixers comprising two CPW-CPS T-junction dual baluns are developed. The bandwidth is about 6:1 without treatment of even mode resonance. After improving the even-mode resonance, the measured relative bandwidths of the star mixers can be larger than 15:1. The planar structure of the circuit is suitable for both MIC and MMIC fabrication. Some MIC prototype circuits are fabricated with an Al/sub 2/O/sub 3/ substrate. The measured conversion losses of the star mixers are about 6 to 10 dB typically within the bandwidth.