Broadband Impedance Transformation by Defected Dielectric on Microstrip Lines

In this work, a different approach to achieve a desired characteristic impedance value on microstrips is presented. In standard microwave circuits using microstrip lines, the dielectric thickness is same and uniform across the whole circuit. In this paper, it is proposed to modify the dielectric thickness to achieve a certain design goal by creating variations in the characteristic impedance of the microstrip transmission line without changing the width of the line. The proposed approach is applied to a multi-section quarter wave impedance transformer. Simulation and measured results demonstrate the potential of the defected dielectric approach by achieving a much wider bandwidth than a conventional multisection impedance transformer. The proposed idea can be expanded and applied to other microstrip based microwave circuits such as filters, power dividers, hybrid couplers, matching networks, etc.