A dual-band balun using coupled stepped-impedance coupled line resonators

In this paper, a novel dual-band balun using a pair of partially coupled stepped-impedance coupled lines is proposed. Design equations for the balun are derived by an even- and odd-mode approach. A prototype of such dual-band balun operating at 900 MHz and 1.8 GHz is designed, fabricated and measured. Good agreement between designed and measured responses proves the proposed concept and validates the design formulae.