A wideband planar microstrip to coplanar stripline transition (balun) at 35 GHz

A novel approach for wideband planar baluns is presented, which enables the realization with just two instead of three transmission lines. The analysis of the principle of operation and a suitable design procedure are described. Measurement results of test structures are compared to EM simulations. Two variants of this balun were designed for a center frequency of 35 GHz. Measurements show an absolute 3 dB-back-to-back insertion loss bandwidth of 16.7 GHz and 10.1 GHz with minimum losses of 0.38 dB and 0.71 dB respectively. The extrapolated absolute 1 dB insertion loss bandwidths of the single baluns are 14.5 GHz and 14.4 GHz respectively.