Effect of tapering shape on performance of broadside-coupled directional couplers

A theoretical model is used to investigate effect of the tapering shape on performance of the broadside-coupled directional coupler. It is shown that the tapering shape has a significant effect on the overall performance. Concave shapes give a broader bandwidth compared with the convex shapes. The model also shows that a proper choice of the tapering shape can result in a significant improvement in the performance across a wide bandwidth. The theoretical findings of the model are supported by simulations, and measurements. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1285-1288. 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.2432