Dual-Band Balanced-to-Unbalanced Power Divider with Inherent Impedance Transformation

A planar microstrip circuit is proposed in this article to design a dual-band balanced-to-unbalanced out-of-phase power divider with inherent impedance transformation. This balanced-to-unbalanced power divider, which essentially consists of two pairs of cascaded coupled lines, two dual-band 90 degrees phase shifters, and a grounded resistor, features the dual-band application with inherent impedance transformation, the equal power division with out of phase, high isolation between two outputs, good ports (A, 3, and 4) matching, and high common-mode noise suppression as well as the excellent conversion inhibition between the differential-mode signals and the common-mode noise. The closed-form solutions are obtained by using the traditional odd-and even-mode analytical methods. Finally, a practical microstrip balanced-to-unbalanced power divider, which operates at 0.9 GHz and 1.8 GHz, is designed and fabricated. The simulated and measured results verify the correctness of the circuit and the design theory.