A substrate integrated waveguide circular cavity (SIWCC) bandpass filter is developed using printed circuit board technology. A circular cavity structure using TM110 mode was employed in the design of the filter to operate at the frequency of 4.75 GHz, which is in the C-band frequency range. The filter was designed based on double-layer elements comprising a substrate integrated circular cavity (SICC) and a transmission line (TL) that produce single-mode resonance. In the proposed structure, circular resonators consisting of vias and a rectangular patch at the top layer are combined into a circular substrate integrated waveguide (SIW) structure. To achieve the desired resonance frequency, a triangle probe is etched at both sides of the microstrip line feeding section. The proposed structure is put in a conducting box to prevent radiation to the outside and eliminate radiation loss. Furthermore, the desired centre frequency and bandwidths of the passbands can be obtained by adjusting the dimension of the filter. To prove the concept, the filter structure is fabricated using Rogers RO4350BTM circuit materials with a dielectric constant of εr = 3.48 and height of the substrate of 1.52 mm. The design was simulated using Ansoft HFSS simulator and measured using a vector network analyser. Simulation and fabrication results are compared for verification. The proposed SIWCC bandpass filter has potential applications in satellites and wireless communication systems.
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