Miniaturization of Triple-Mode Wideband Bandpass Filters

In this article, a class of wideband bandpass filters (BPFs) using triple-mode coaxial resonators has been introduced. Each triple-mode resonator is utilized with TM
₀₁₀
mode, TE− mode, and TE+ mode orthogonal to each other. Two L-shaped feeding probes and a loading disk are adopted to implement the miniaturization of these wideband BPFs. To observe the degree of miniaturization, we set a design specification of the same fractional bandwidth (FBW) of 40% at the same central frequency of 2.5 GHz. After employing the L-shaped feeding probes and loading disk, the efficient circuit size without cavity thickness is reduced by 80% compared with the triple-mode wideband filter without L-shaped feeding probes and loading disk. In contrast, the unloaded quality factors are slightly changed. In addition, another advantage of this work is that the upper stopband is extended to
$2.5f_{0}$
. Three experimental wideband BPFs in the large, medium, and small sizes are designed, manufactured, and tested for demonstration. Good agreements are obtained between simulation and experiment.