Design of Compact Quad-Frequency Impedance Transformer Using Two-Section Coupled Line

This paper presents a compact quad-frequency impedance transformer that is composed of a two-section coupled line to achieve ideal impedance matching at three arbitrary frequencies and a related frequency. The exact closed-form equations and design procedures are given based on strict theoretical analysis. After demonstrating the bandwidth performance and symmetry properties of different impedance transform ratios, we fabricated a circuit to show the validity of practical applications. Good agreement between the measured data and anticipated results is achieved.