Via-free microstrip to slotline baluns using slotted microstrip cross-junction

This paper presents two novel microstrip-to-slotline baluns. Their design is based on the slotted microstrip cross-junction and its multi-mode equivalent circuit model, i.e., each slotted microstrip supports two modes that have even and odd symmetry. The first balun is a modified version of the conventional 90° via-less microstrip to slotline one with different microstrip and slotline impedances. The 3 dB bandwidth is 2.44 GHz and the minimum insertion loss is 0.5 dB at 2.4 GHz. The second balun is a via-less straight microstrip-to-slotline one that has 3 dB bandwidth of 2.29 GHz and minimum insertion loss of 0.46 dB at 2.4 GHz. Theoretical predictions have been confirmed by EM simulations and measurements.