Analysis of quadruple corner-cut ridged square waveguide by hybrid mode-matching boundary-element method

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 TE20 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 (C) 2010 John Wiley & Sons, Ltd.