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A miniaturized wideband coupled-line microstrip balun using a new defected ground



This letter proposes a new miniaturized wideband coupled-line microstrip balun and its design procedure based on an original finding. This finding suggests that the coupled-line microstrip balun can be realized by using a much smaller high-pass ground defect instead of a bandstop ground defect. The newly proposed balun is derived initially from a coupled-line microstrip balun with a typical dumbbell-shaped defected ground. Following the proposed three-step design procedure, the size of the final balun is only about 8.3% of the size of the initial one (only 0.00512 wavelength square at the central frequency). In addition, the final balun possesses immunity against the influence of the supporting material. Balun prototypes were created and investigated. Both the simulated and measured results demonstrate the compactness and wideband performance. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:254–257, 2012; View this article online at DOI 10.1002/mop.26518