A new formula for the effective width design of substrate integrated waveguide (SIW) structures is presented. Contrary to another formulation of similar accuracy, which requires an iterative process or solution of a fifth-order polynomial, the new equation allows the direct design of the SIW's width for a given cutoff frequency. The presented formula is obtained by minimizing the reflections from the junction between the SIW and an all-dielectric waveguide of equivalent width. A mode-matching approach is used to derive the equation which is verified by comparison with WaveWizard for three SIW examples. Further optimizations in CST Microwave Studio and WaveWizard demonstrate the robustness of the new formula. Index Terms-Design equation, effective waveguide width, mode-matching techniques (MMTs), substrate integrated waveguide (SIW).

A new wideband transition from microstrip line to substrate integrated waveguide (SIW) is introduced. Unlike most transitions that show reduced return loss over significant parts of a regular waveguide band, the presented configuration achieves return losses better than 30 dB in standard waveguide frequency bands from X to E. The new aspect of this transition is the addition of two vias to the widely used microstrip taper transition. Moreover, the influence of the substrate height is demonstrated. The results in each frequency band are compared with the data for the regular microstrip taper alone. A design formula for the placement of the vias and taper dimensions is presented and demonstrated to provide excellent results. The structures are simulated and optimized with CST Microwave Studio. Measurements performed on a Ku-band back-to-back prototype transition demonstrate a minimum return loss of 26.05 dB and maximum insertion loss of 0.821 dB over the entire Ku-band, thus validating the design approach.

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A mode-matching approach is presented that allows a fast and accurate analysis of substrate-integrated wave-guide components with rectangular/square via holes. Models for several discontinuities are discussed which include microstrip as well as all-dielectric wave-guide feeds. The numerical technique is verified by comparison with commercially available field solvers. An example of a fourpole dual-mode filter in substrate-integrated wave-guide technology illustrates the capabilities of the approach.