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Abstract <p>This paper considers the design and investigation of a quasi-elliptic bandpass filter implemented on the basis of a rectangular waveguide and its equivalent realization in the form of a substrate integrated waveguide (SIW) structure. The aim of the study is to reduce the mass–dimensional parameters of a classical waveguide filter while preserving the high quality factor and frequency selectivity required for modern communication systems. As a prototype, a four-resonator bandpass filter in a WR-137 rectangular waveguide with quarter-wavelength couplings is used. For this filter, a quasi-elliptic amplitude–frequency response with transmission poles and transmission zeros in the vicinity of the passband is synthesized by means of full-wave electromagnetic simulation. It is shown that the introduction of an additional electric cross-coupling based on a capacitive iris makes it possible to significantly improve the steepness of the response and the suppression of out-of-band signals. Subsequently, the geometrical parameters of the folded waveguide filter are transformed into an equivalent SIW configuration on an FR-4 substrate, implemented using standard printed-circuit technology. Three-dimensional electromagnetic simulation in CST Microwave Studio is carried out, and a prototype is fabricated using a CNC milling machine. Comparison of the simulated and measured amplitude–frequency responses demonstrates good agreement, which confirms the correctness of the synthesis procedure and the high reproducibility of the proposed design. A 34% reduction of the longitudinal size of the filter is achieved while maintaining the shape of the frequency response and an insertion-loss level comparable to that of the waveguide prototype. The obtained results demonstrate the feasibility of transitioning from classical waveguide filters to compact SIW devices with an almost fully shielded structure, promising for applications in telecommunication and radar systems. Special attention is paid to the influence of variations of geometrical parameters on the frequency response, which is important for ensuring technological robustness and series production of the developed filters.</p>

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Compact Quasi-Elliptic SIW Filter Equivalent to a Waveguide Structure: Size Reduction While Preserving High-Quality Frequency Response

  • 期刊论文

  • 发表日期：

    2026年3月1日

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  • S. V. Krutiev,
  • S. P. Bukin,
  • D. S. Gubskiy,
  • M. A. Samoletova

摘要

Abstract

This paper considers the design and investigation of a quasi-elliptic bandpass filter implemented on the basis of a rectangular waveguide and its equivalent realization in the form of a substrate integrated waveguide (SIW) structure. The aim of the study is to reduce the mass–dimensional parameters of a classical waveguide filter while preserving the high quality factor and frequency selectivity required for modern communication systems. As a prototype, a four-resonator bandpass filter in a WR-137 rectangular waveguide with quarter-wavelength couplings is used. For this filter, a quasi-elliptic amplitude–frequency response with transmission poles and transmission zeros in the vicinity of the passband is synthesized by means of full-wave electromagnetic simulation. It is shown that the introduction of an additional electric cross-coupling based on a capacitive iris makes it possible to significantly improve the steepness of the response and the suppression of out-of-band signals. Subsequently, the geometrical parameters of the folded waveguide filter are transformed into an equivalent SIW configuration on an FR-4 substrate, implemented using standard printed-circuit technology. Three-dimensional electromagnetic simulation in CST Microwave Studio is carried out, and a prototype is fabricated using a CNC milling machine. Comparison of the simulated and measured amplitude–frequency responses demonstrates good agreement, which confirms the correctness of the synthesis procedure and the high reproducibility of the proposed design. A 34% reduction of the longitudinal size of the filter is achieved while maintaining the shape of the frequency response and an insertion-loss level comparable to that of the waveguide prototype. The obtained results demonstrate the feasibility of transitioning from classical waveguide filters to compact SIW devices with an almost fully shielded structure, promising for applications in telecommunication and radar systems. Special attention is paid to the influence of variations of geometrical parameters on the frequency response, which is important for ensuring technological robustness and series production of the developed filters.