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International Journal of Antennas and Propagation
Volume 2014, Article ID 803515, 9 pages
Research Article

Analysis of a Substrate Integrated Waveguide Hybrid Ring (Rat-Race) Coupler

1Department of Electrical Engineering, Science and Research Branch, Faculty of Engineering, Islamic Azad University, Tehran 14778 93855, Iran
2Department of Electrical Engineering, Faculty of Engineering, Tarbiat Modares University (TMU), Tehran 14115 111, Iran

Received 24 January 2014; Revised 4 April 2014; Accepted 4 April 2014; Published 28 April 2014

Academic Editor: Francisco Falcone

Copyright © 2014 Ramin Dehdasht-Heydari et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper presents an efficient analysis of a substrate integrated waveguide (SIW) single-layer hybrid ring coupler (rat-race) for millimeter-wave and microwave applications. The scattered field from each circular cylinder is expanded by cylindrical eigenfunctions with unknown coefficients that have been solved by electric and magnetic tangential boundary on each metallic via. The coupler S-matrix is calculated by using mode matching that uses the cylindrical vector expansion analysis to minimize the computational time and provides more physical insight. To achieve higher bandwidth, the radiuses of the coupler under analysis have been optimized in Matlab code by invasive weed optimization (IWO) method, and the results have been verified by CST package. The return loss and the isolation are less than −15 dB, and −18 dB, respectively. The insertion loss is divided equally  dB, with and degrees in output ports over the operating frequency bandwidth and the agreement of phase differences in output ports has been examined objectively by feature selective validation (FSV) technique.