Short-Ended Coupled-Line Impedance Transformers With Ultrahigh Transforming Ratio and Bandpass Selectivity Suitable for Large Load Impedances

In this paper, a class of short-ended coupled-line impedance transformers with ultrahigh transforming ratio is proposed. The principle for the realization of such an ultrahigh transforming ratio is first illustrated using a one-section coupled line. Then, multisection coupled lines are used to further broaden their operating bandwidth by virtue of our presented design method. In this regard, various sets of design curves are provided to demonstrate the characteristics of these impedance transformers and to execute their design and implementation on the microstrip-line structure. In addition to impedance transformation, the proposed impedance transformers exhibit their attractive bandpass filtering characteristics. Finally, two 50-1000-Ω impedance transformers are designed and fabricated based on two- and three-section short-ended coupled lines to provide the experimental verification on the predicted results.