volume | PIER Journals

Abstract

To suppress multiple narrowband interferences in ultra-wideband (UWB) communication systems while maintaining a compact size and wide passband response, a quad-notch ultra-wideband filter based on a bowtie T-shaped resonator is proposed and investigated. The proposed filter employs an improved stepped-impedance resonator (SIR) with multi-branch loading and an annular defected ground structure (DGS) to enhance bandwidth extension, passband flatness, and frequency selectivity. A novel quasi-closed-loop C-shaped resonator with an additional coupling path is introduced to generate an extra controllable resonant mode, providing enhanced flexibility for independent notch-band tuning. Combined with an asymmetric open-circuited branch, four independently adjustable notch bands are achieved within the UWB passband. The resonance characteristics of the proposed multimode structure are analyzed using even-odd mode theory, providing an effective approach for mode-frequency control. Experimental results demonstrate that the fabricated filter achieves a wide passband from 2.71 to 11.5 GHz with a fractional bandwidth of 124%, along with four sharp rejection bands centered at 5.91, 6.75, 7.29, and 8.08 GHz. The maximum attenuation reaches 34.55 dB, while the filter maintains a compact size of 23 mm × 29.74 mm with excellent passband flatness and out-of-band suppression. The proposed quad-notch UWB filter provides an effective solution for interference-resistant wireless communication systems.

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Dr. Mingming Gao

Dr. Ke Li

Dr. Maoyuan Wei