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New ultra-wideband high-order Marchand baluns with one microstrip unbalanced port and two microstrip balanced ports are proposed in this paper. The proposed Marchand baluns are synthesized based on an -plane high-pass prototype using the Richards' transformation. The responses of the synthesized high-order Marchand baluns are exactly predicted at all real frequencies. All circuit elements are commensurate, which means the electrical lengths of all transmission line elements are a quarter-wavelength long at the center frequency. Two fifth-order Marchand baluns with reflection coefficients of 20.53 and 21.71 dB corresponding to 131% and 152% bandwidth, respectively, are synthesized and realized using the combinations of microstrip lines, slotlines, and coplanar striplines. Simulated and measured results are presented.