INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS Int. J. Numer. Model. 2011; 24:24–35 Published online 26 April 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jnm.758 Analysis of quadruple corner-cut ridged square waveguide by hybrid mode-matching boundary-element method Yun Tao, Zhongxiang Shen Ã,y and Boyu Zheng School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore SUMMARY In this paper, the square waveguide with quadruple corner-cut ridges is analyzed using the hybrid mode- matching boundary-element method. Because of its symmetry, only a quarter of its cross-section needs to be considered and it is then divided into three regions. The electromagnetic field components in two regular regions can be obtained using the mode-matching method and the third irregular region is discretized using the boundary-element method. The combination of two methods produces one matrix equation, from whose determinant the cutoff wavenumbers of waveguide modes can then be computed. This hybrid technique takes advantage of the mode-matching method’s high efficiency and the boundary-element method’s versatility. The convergence of this hybrid method is studied, and numerical results are compared with the conventional boundary-element method and commercial finite-element software package, which shows that our hybrid method can achieve the same accuracy with much less time. The influence of the cut- corners on the cutoff wavenumbers of the dominant and higher-order modes is then examined. A simple approximate equation is found to accurately predict the cutoff wavenumber of TE 20 mode. The single- mode bandwidth of a quadruple ridged square waveguide is calculated thereafter, which shows that this corner-cut structure can provide a broader bandwidth compared to the one without cut-corners. Copyright r 2010 John Wiley & Sons, Ltd. Received 16 October 2008; Revised 20 January 2010; Accepted 2 February 2010 KEY WORDS: ridged waveguide; hybrid technique; boundary-element method; mode-matching method 1. INTRODUCTION Ridge waveguide [1] has been extensively used in microwave and antenna systems because of its low cutoff frequency, wide single-mode operation bandwidth, and low impedance compared to the conventional rectangular waveguide [1, 2]. As modern communication systems require higher and higher capacity, the quadruple-ridged waveguides are widely employed because of their natural characteristic of supporting dual polarizations [3, 4]. The characteristics of a quadruple-ridged waveguide have been studied by the finite-element method (FEM) [5] and the magnetic field integral equation (MFIE) method [6]. The cutoff wavenumbers and field distributions of several lowest modes in a quadruple-ridged waveguide were obtained. In practical applications, the quadruple ridges in a square waveguide are usually cut at their corners [3, 4], as shown in Figure 1. This is to substantially lower the cutoff frequency of the *Correspondence to: Zhongxiang Shen, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. y E-mail: ezxshen@ntu.edu.sg Copyright r 2010 John Wiley & Sons, Ltd.