3D Manufactured Stepped-Impedance Microwave Filter with Improved Stop-band
Ahmed, Estiaq (2025)
2025
Sähkötekniikan DI-ohjelma - Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
Hyväksymispäivämäärä
2025-12-29
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-2025122912222
https://urn.fi/URN:NBN:fi:tuni-2025122912222
Tiivistelmä
Standard microstrip filters on cheap FR-4 substrates usually suffers from weak stop-band rejection, high insertion loss, and significant parasitic radiation. To address these issues, the research in this thesis proposes the design, simulation, and fabrication of a compact stepped-impedance low-pass filter that achieved a better stop-band attenuation and improved return loss characteristics compared to conventional planar filters on lossy substrates.
The design integrates theoretical synthesis with full-wave electromagnetic modelling. Initial LC prototype values were calculated for 1.85 GHz cut-off frequency using the Marki Microwave design tool. The experiment followed by transmission-line synthesis in Keysight ADS to determine physical geometry of the filter. The filter was then converted into a microstrip circuit to compare their stop-band response. It was designed in Ansys HFSS, simulated, and fabricated on 0.8 mm FR-4 substrate. Since the measured result produced weak stop-band attenuation, a 3D approach with reduced substrate thickness in low-impedance sections was introduced. The design was modelled again in ADS, and HFSS and fabricated using PCB milling followed by conductive cavity coating.
Measurement of the final filter showed a cut-off frequency of approximately 1.60 GHz, and more than –26 dB attenuation at 2.45 GHz, with a stable stop-band below –30 dB across 20 GHz frequency range. The result confirms that 3D structuring offer an effective and practical method to improve the performance of stepped-impedance filters on FR-4 substrates.
The design integrates theoretical synthesis with full-wave electromagnetic modelling. Initial LC prototype values were calculated for 1.85 GHz cut-off frequency using the Marki Microwave design tool. The experiment followed by transmission-line synthesis in Keysight ADS to determine physical geometry of the filter. The filter was then converted into a microstrip circuit to compare their stop-band response. It was designed in Ansys HFSS, simulated, and fabricated on 0.8 mm FR-4 substrate. Since the measured result produced weak stop-band attenuation, a 3D approach with reduced substrate thickness in low-impedance sections was introduced. The design was modelled again in ADS, and HFSS and fabricated using PCB milling followed by conductive cavity coating.
Measurement of the final filter showed a cut-off frequency of approximately 1.60 GHz, and more than –26 dB attenuation at 2.45 GHz, with a stable stop-band below –30 dB across 20 GHz frequency range. The result confirms that 3D structuring offer an effective and practical method to improve the performance of stepped-impedance filters on FR-4 substrates.