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 TM₀₁₀ 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 2.5 f₀. 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.