An ultra-wideband (UWB) bandpass filter with microstrip-to-CPW transition and a notch-band

An ultra-wideband (UWB) bandpass filter is proposed in this paper. The proposed structure composes of two pairs of microstrip short-circuited stubs which provide a microstrip-to-CPW transition, and a CPW resonator whose length is about half-guided-wavelength (λ_g/2) at 6.85GHz. A triple-mode UWB bandpass filter is produced using this microstrip-to-CPW transition structure. In order to suppress WLAN signals around 5.2/5.8GHz, a novel via-stub-loaded structure is designed. By adding this via-stub-loaded structure, a bandstop characteristic is formed as a notch-band whose position and bandwidth could be tuned easily. Simulation results indicate that the reflection loss is lower than -15dB in desired passband, and it also achieves a good performance of the notch-band around 5.2/5.8GHz. Finally, the proposed UWB bandpass filter is fabricated and measured. The measured results are in good agreement with simulated ones.