High Impedance Transforming Dual-Band Balun with Isolation and Output Ports Matching

A dual-band balun with inherent impedance transformation is presented in this paper. The inherent impedance transformation ratio from a range of 0.4 to 4.0 makes the balun ideal for the on-chip fabrication. The proposed dual-band balun exhibits excellent input port matching, equal output signal with phase difference of 180 degrees, and extremely good isolation and matching at the output ports. A table is provided with the design parameters at the extreme impedance transformation ratios. The design concept of the proposed balun has been validated through a prototype fabricated on a Rogers RO5880 substrate. The measurement results are in good agreement with the EM simulation measurements.