Substrate Integrated Waveguide Based 5G Bandpass Filter - Design and Implementation
Ifty, Hadi Istiak Ahmed (2025)
2025
Sähkötekniikan DI-ohjelma - Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2025-12-23
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-2025122312109
https://urn.fi/URN:NBN:fi:tuni-2025122312109
Tiivistelmä
Microwave systems rely on fundamental components such as filters, couplers, and dividers. At higher frequencies, lumped elements become impractical, and distributed implementations are required. While microstrip devices offer compactness, their performance degrades at millimeter-wave bands due to increased radiation losses, making conventional waveguides preferable but often bulky and costly. Substrate integrated waveguide (SIW) technology overcomes these limitations by providing a low-cost, lightweight, and planar realization of waveguides, well suited for integration with modern microwave circuits.
This thesis presents the design, analysis, and experimental validation of SIW-based Complementary Split Ring Resonator (CSRR)-type bandpass filters. An SIW bandpass filter is developed for 5G X-band in the 8.2-12.4 GHz frequency band, more specifically targeting to cover the 10.7 to 11.7 GHz 5G backhaul window. Magnetic coupling between adjacent CSRRs is achieved through optimised openings, enabling precise control of the filter response. Upon evaluating the fabricated prototype using a Vector Network Analyser (VNA), the filter's frequency response exposes a centre frequency of 10.95 GHz, spanning from 10.23 GHz to 11.71 GHz, with a recorded fractional bandwidth of 13.51%, an insertion loss of 2.9 dB, and an in-band return loss exceeding 30.61 dB. The frequency response of the simulated design filter exhibits a 3 dB bandwidth of 1.71 GHz (ranging from 10.21 GHz to 11.92 GHz), with a centre frequency of 11.03 GHz, an insertion loss of 1 dB, and an in-band return loss of 28.07 dB.
Simulation and measurement results show good agreement in terms of passband location and overall bandwidth, confirming the fundamental operability of the proposed filter. The fabricated prototype exhibits a slightly shifted response and higher insertion loss than the ideal model due mainly to uneven soldered via-stitches, parasitic and leakage, which also generate ripples and nearby side passbands. A deeper analysis of these imperfections motivated a new SIW case study where via density and CSRR cavity splits are systematically modified. The optimised cases cover the 10.7 to 11.7 GHz window with lower simulated insertion loss and better passband suppression. Thus, the prototype and refined case design are promising candidates for next generation 5G backhaul applications due to their compact, single-layer structure, simple PCB fabrication, and easy integration into modern RF technology.
This thesis presents the design, analysis, and experimental validation of SIW-based Complementary Split Ring Resonator (CSRR)-type bandpass filters. An SIW bandpass filter is developed for 5G X-band in the 8.2-12.4 GHz frequency band, more specifically targeting to cover the 10.7 to 11.7 GHz 5G backhaul window. Magnetic coupling between adjacent CSRRs is achieved through optimised openings, enabling precise control of the filter response. Upon evaluating the fabricated prototype using a Vector Network Analyser (VNA), the filter's frequency response exposes a centre frequency of 10.95 GHz, spanning from 10.23 GHz to 11.71 GHz, with a recorded fractional bandwidth of 13.51%, an insertion loss of 2.9 dB, and an in-band return loss exceeding 30.61 dB. The frequency response of the simulated design filter exhibits a 3 dB bandwidth of 1.71 GHz (ranging from 10.21 GHz to 11.92 GHz), with a centre frequency of 11.03 GHz, an insertion loss of 1 dB, and an in-band return loss of 28.07 dB.
Simulation and measurement results show good agreement in terms of passband location and overall bandwidth, confirming the fundamental operability of the proposed filter. The fabricated prototype exhibits a slightly shifted response and higher insertion loss than the ideal model due mainly to uneven soldered via-stitches, parasitic and leakage, which also generate ripples and nearby side passbands. A deeper analysis of these imperfections motivated a new SIW case study where via density and CSRR cavity splits are systematically modified. The optimised cases cover the 10.7 to 11.7 GHz window with lower simulated insertion loss and better passband suppression. Thus, the prototype and refined case design are promising candidates for next generation 5G backhaul applications due to their compact, single-layer structure, simple PCB fabrication, and easy integration into modern RF technology.