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Planar-type Marchand baluns are embedded into on-wafer probes in order to provide accurate differential measurement capabilities for conventional single-ended measurement equipments such as the two-port vector network analyzer. In designing the planar-type Marchand balun, the values for differential- and common-mode characteristic impedances of the coupled transmission lines are analytically derived by using general transmission line theories. The derived characteristic impedances are realized using a double-sided single-layer printed circuit board surrounded by conductive fixtures. The proposed coupled transmission line structure provides convenient port interfaces to the coaxial cables and it is free from bond wires and vias, enabling one to achieve high cost efficiency and reproducibility.