Stepped coupled-line balun design for enhanced bandwidth operation

This letter presents a practical design method for the stepped impedance coupled-line balun using an effective and simple way to increase the balanced output bandwidth of the coupled lines in the conventional planar Marchand balun. A new structure of collateral multi-section with quarter wavelength coupled-line balun is developed to increase at least 40% more balanced bandwidth and to achieve a better return loss than the traditional planar Marchand coupled-line balun. The structure of the designed planar microstrip circuit is fairly simple, practical and easy to fabricate. The measured results of the design show fine agreements with the simulated data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1877–1879, 2007; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.22585