For the purpose of providing faster CAD algorithms for substrate-integrated waveguide (SIW) filter design, an efficient mode-matching technique uses a model to convert circular via holes to square shapes. It is demonstrated that a conversion based on the side length of the equivalent square via being equal to the arithmetic mean of the side lengths of the inscribed and circumscribed squares of the circular via provides results acceptable even for advanced filter design procedures. Several

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... examples using the SIW equivalents of metal-insert, inductive-iris and H-plane quasi-elliptic waveguide filters are designed using the mode-matching technique with square via holes. The results are then verified by commercially available field solvers modeling the respective filters with circular via holes. A final comparison with measurements verifies the design procedure in practical applications.