Search

This paper proposes a novel planar dual-band coupled-line balun with impedance transformation and high isolation. Closed-form design equations are obtained based on the classical even-odd mode equivalent approach. For convenience of designing and synthesizing such a novel dual-band balun, the practical ranges of the frequency ratio, terminated impedances, and two free variables are provided under the conventional microstrip fabrication constraints. By adopting four coupled-line sections, six transmission-line stubs, and an isolation resistor, a microstrip prototype balun working at 1.0/2.6 GHz is designed, fabricated, and measured. There is a good agreement between the simulated and measured results. The wide bandwidths of 290 MHz from 0.83 to 1.12 GHz and 270 MHz from 2.44 to 2.71 GHz are obtained with the measured return losses (|S11|, |S22|, |S33|) and the isolation (|S23|) better than 10 dB, which effectively confirm the proposed theoretical predictions.

This letter presents a practical and simple uniplanar coupled-line balun with lower profile coplanar waveguide (CPW) structure to enhance the coupled coefficient and balanced output bandwidth for millimeter-wave operations. The CPW balun with a pair of symmetric quarter wavelength coupled lines is developed to increase at least 150% (1.5 times) bandwidth efficiency with a return loss better than the traditional planar coupled-line balun. The structure of the designed balun is simple, practical, and easy to fabricate. The measured results show fine agreements with the simulated data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2902–2905, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22926 [ABSTRACT FROM AUTHOR]