Over-Moded Transverse Magnetic Cavity Filters for Narrowband Millimeter-Wave Applications

A new version of transverse magnetic (TM) cavity filters for high-frequency applications is presented in this letter. The basic building block of these filters is the over-moded transverse magnetic cavity (OTMC). The OTMC supports a pair of high-order resonant modes, namely TM₃₂₀ and TM₂₃₀, as well as various nonresonating modes that can be exploited to provide an additional input-to-output path (the propagating TM₁₁ is the one primarily employed in the particular configuration here presented). Besides the possibility of realizing elliptic responses having the maximum number of transmission zeroes, a higher Q-factor as well as a significantly reduced sensitivity to manufacturing imperfections is the main benefit making these structures especially suitable for the practical realization of very narrowband millimeter-wave filters. The experimental results of an elliptic fourth-order OTMC filter with 0.2% fractional bandwidth at 41.415 GHz validate the feasibility of these new transverse magnetic filters.