DESIGN OF A DUAL-BAND MICROSTRIP BRANCH-LINE BALUN USING T-SHAPED COUPLED LINES

摘要

This article presents the development of a novel dual-band branch line balun with design flexibility. The T-shaped coupled line structure is constructed by two series short-ended coupled lines and one open-ended stub to obtain the dual-band characteristics. The proposed dual-band structure has the capability to design a conventional microstrip line with arbitrary impedances and electrical lengths at two different operating frequencies. In addition to this, different range of frequency ratios is obtained by varying the length of the stub. The required explicit design equations are derived analytically to compute the physical dimensions of the coupled lines and stub. Based on these equations, closely and widely spaced frequency bands useful for many wireless communication systems are devised. To prove better agility, three examples of dual-band branch line baluns are designed. Finally, a prototype of dual-band balun is demonstrated for GSM and WiMAX applications at 0.9 and 3.5 GHz, respectively. Good agreement is found between the theoretical predictions and experimental results. (C) 2017 Wiley Periodicals, Inc.