On-substrate resonant cavity / Mohd Fikri Shakirin

The resonant frequency of the circular cross-sectional FR4-filled cavity is studied and presented in this paper. The cavity model is designed within the two layers of the FR4 substrate with the permittivity of 4.1. The feed lines are located between the two layers of the substrate while the circular cavity is surrounded by the metallic via. The dimensions are set such as to have a fundamental resonant frequency at about 4.610 GHz. Dominant TMoio and TEJH modes wave are excited into the cavity to give various value the resonant frequency depending on the radius of the circular cavity. The simulation results show that the resonant frequency of the cavity resonator decreases dramatically as the radius of the circular cavity increased for TMoio mode. Differ to the TEm mode which is resonant frequency decreased slightly as the radius of the circular cavity increased. The best radius of the circular cavity is found to be 12.3mm, giving the closest resonant frequency to the one desired. The metallic via around the circular plate is to emulate the metallic wall a normal cavity where their distance is kept minimum to reduce leakage loss through giving the clear resonance variation. The works show very close agreement between the result from simulation and the measurement. The success of the project may lead to the possibility of using planar structure to emulate resonant cavity for filters.