Reconfigurable Cavity Bandpass Filters Using Fluid Dielectric

A novel method for the development of a reconfigurable cavity bandpass filter using fluid dielectric is proposed. Dielectric material can produce an effective permittivity <italic>ϵ</italic>_eff of the resonant mode when it is loaded into the cavity. Thus, a tube filled with fluid dielectric, e.g., distilled water, can achieve controlled and reversible <italic>ϵ</italic>_eff by adjusting the amount of water in the tube. The same manner of resonant frequency can be achieved as the resonant frequency is related to <italic>ϵ</italic>_eff, and then frequency tuning is realized. The fluid property can realize easier and faster tuning mechanism than conventional solid dielectric. As <italic>ϵ</italic>_eff is affected by the loaded dielectric parallel to the electric field, a triple-mode resonator with resonant modes TE₁₀₁, TE₀₁₁, and TM₁₁₀, which have orthogonal electric fields, is investigated to realize tri-band reconfiguration. The <italic>ϵ</italic>_eff, as well as the resonant frequencies, corresponding to each mode can be individually controlled by adjusting their related water posts. Then, reconfigurable single-band and tri-band bandpass filters are designed. A reconfigurable tri-band cavity filter using a triple-mode cavity resonator and fluid dielectric with individual and continuous frequency tuning is reported for the first time. Finally, the reconfigurable tri-band filter is fabricated and measured to validate the concept.