Compact UWB Bandpass Filter based on Crossed Dumbbell-Stub with Notch Band using Defected Microstrip Structure

A compact ultra-wideband (UWB) bandpass filter based on cross dumbbell stub with notch band structures is proposed and implemented. This bandpass filter (BPF) structure consists of directly feed line input/output. As the novelty, the cross dumbbell stub resonator was used and it was placed at the middle of the filter structure. By using this structure, the BPF not only has a compact size but also it has a wide-passband response. To remove unnecessary radio frequency (RF) signal, the rejection (notch) band was also proposed by using a novel technique which uses U-shaped defected microstrip structure (DMS). Moreover, the DMS is constructed at the center between crossed dumbbell resonators. This notch band structure has highly independent and it can be adjusted by modifying the U-shaped structure. Therefore, the specific frequency of the notch band can be selected independently without expanded number of resonator or stub. Furthermore, this BPF is fabricated on 2D - Duroid/RT 5880 substrate with permittivity (εr) of 2.2, thickness (h) of 1.57 mm, and loss tangent tand of 0.0009. Furthermore, the measured results show that the UWB-BPF has 3-dB passband from 3.0 - 12.2 GHz, with notch band at 6.7 GHz and the notch band has attenuation -22 dB. The design structure was verified by a good agreement between simulated and measured result. Overall, the proposed filter design has excellent performance in term of insertion loss, high independent notch-band, compact size, and implementable structures.