A New Design Method for Unequal Dual-Band Modified Wilkinson Power Divider

A new design method for a dual-band (or dual-frequency) modified Wilkinson power divider with an unequal power dividing ratio is proposed in this article. First, a dual-band transformer with a flexible transmission line stub, which can be fabricated by a shorted-circuit stub or an open-circuit stub, for two arbitrary real impedances is analyzed, and the rigorous design method is obtained. It is necessary to apply the asymmetric structure in all unequal power dividers in order to obtain unequal power dividing; thus, an asymmetric structure, which consists of two equivalent asymmetric dual-band transformers with a parallel transmission line stub in the input matching part, is developed for an unequal dual-band power divider. A resistor is then used in this proposed power divider, as the effective isolation structure to obtain ideal isolation between two output ports while two-section transmission line transformers are applied to match impedances at two output ports. In the synthesis procedure, two groups of closed-form design equations of this unequal dual-band power divider without reactive lumped-elements are given. Furthermore, simulations of two sample examples have verified the new structure and the design method for this power divider in theory. Finally, a practical microstrip power divider, which operates at both 0.95 GHz and 2.28 GHz with 3 dB power dividing ratio, is designed, fabricated and tested. There are good agreements between the simulated and measured results.