Design Approach for Bandpass Filters Based on Enhanced Iris Model: Applications to TE ₂₀₁ Singlets and TE ₂₀₁ /TE ₁₀₂ Cavities in Rectangular Waveguide

This article presents a novel design methodology for bandpass filters applied to rectangular waveguide (RW) technology using TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> singlets and TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub>/TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> dual-mode cavities. The conventional circuit model for an inductive iris interconnecting two RW sections, which typically handles only the TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode, is extended to include the propagation of the TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode through a wider RW section. The impact of the reactances at the source and load terminals of the circuit model is analyzed to develop a unique solution for the coupling matrix (CM) synthesis. The proposed methodology improves design flexibility, allowing for filters with both cascaded singlet and cascaded triplet topologies. This is demonstrated through two illustrative designs. The first design employs propagating RW sections as phase shifters to interconnect TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> singlets, which is the most common approach. The second design, however, replaces these sections with TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> resonant cavities. This substitution offers advantages in spurious-free range, volume, and mass. Both prototypes were successfully manufactured and measured to validate the approach experimentally. The validity of the enhanced iris model is also extended to the design of bandpass filters using TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub>/TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> dual-mode cavities.