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A novel method for the development of a reconfigurable cavity bandpass filter using fluid dielectric is proposed. Dielectric material can produce an effective permittivity ϵeff 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 ϵeff 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 ϵeff, and then frequency tuning is realized. The fluid property can realize easier and faster tuning mechanism than conventional solid dielectric. As ϵeff 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 ϵeff, 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. [ABSTRACT FROM AUTHOR]

In this paper, a series of designs for cavity balanced and unbalanced diplexer are proposed. The balanced and unbalanced designs can be categorized into four groups—unbalanced-to-unbalanced, unbalanced-to-balanced, balanced-to-unbalanced (B2U), and balanced-to-balanced. First, two approaches to achieve out-of-phase characteristics of three fundamental modes, namely TE011, TE101, and TM110 in a single triple-mode resonator, are proposed for balun filter designs. Second, four types of unbalanced and balanced diplexers are presented by adopting these three fundamental modes, of which the Butterworth response applies with specific external quality and coupling coefficient. To the authors’ best knowledge, full-metal cavity balun diplexer and balanced diplexer are not reported in the open literature. For proof of concept, the design of a B2U diplexer is fabricated and measured. Good matching between simulated and measured results shows the accuracy of the proposed design and methodology, which would be attractive in the high-power radio frequency (RF) front-end systems. [ABSTRACT FROM AUTHOR]