# Parallel-Coupled-Line Bandpass Filter with Notch for Ultra-Wideband (UWB) Applications
## 5 Conclusions  
This article introduced a compact microstrip parallel-coupled-line bandpass filter with an ultra-wideband (UWB) passband and a narrow notched band. The presented UWB bandpass filter was developed by using three parallel-coupled-line sections. The electrical length of the coupled lines was designed to be a quarter-wavelength at approximately 6.9 GHz midband frequency. A very high selectivity was achieved using additional short-circuited stubs, which generated a transmission zero at the lower and upper rejection bands close to the desired UWB passband edges. In order to generate a notch with a narrow band inside the passband to reject the unwanted WLAN signal, a stepped-impedance resonator was coupled to the three parallel-coupled line sections. The fabricated filter showed an excellent agreement between the measured and the full-wave electromagnetic simulated performances. The measured insertion loss was very low along the entire UWB passband. The fabricated UWB filter is very compact compared to other filters in the literature.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref.** & **Passband (GHz)** & **FBW (\%)** & **S11 (dB)** & **S21 (dB)** & **Circuit Size (\(\lambda_{g}\)\(\times\)\(\lambda_{g}\))** \\ \hline
[2] & 1.83–3.16 & 53 & \textgreater{}14 & \textless{}1.0 & 0.62 \(\times\) 0.25 \\
[3] & 2.96–10.67 & 113 & \textgreater{}10 & \textless{}2.0 & 0.35 \(\times\) 0.05 \\
[4] & 2.8–10.27 & 112 & \textgreater{}14 & \textless{}1.4 & 0.32 \(\times\) 0.07 \\
[5] & 2.8–11.0 & 119 & \textgreater{}10 & \textless{}1.1 & 0.22 \(\times\) 0.16 \\
[6] & 2.8–11.2 & 120 & \textgreater{}12 & \textless{}2.0 & 0.61 \(\times\) 0.23 \\
[7] & 3.1–11.1 & 117 & \textgreater{}10 & \textless{}1.5 & 0.51 \(\times\) 0.34 \\
[8] & 1.0–20.0 & 180 & \textgreater{}10 & \textless{}0.6 & 0.8 \(\times\) 0.22 \\ This work & 3.1–10.7 & 110 & \textgreater{}12 & \textless{}0.9 & 0.096 \(\times\) 0.08 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results comparison with other UWB filters.  
Figure 16: Comparison between full-wave EM-simulated and measured insertion and return losses for the presented filter with a notch: (**a**) (S21) and (**b**) (S11).  
Figure 17: Comparison between the group delay of the simulated and measured filter.  
**Author Contributions:** Conceptualization, G.H.A., F.H.A. and H.N.S.; methodology, G.H.A. and F.H.A.; software, G.H.A. and F.H.A.; analysis, G.H.A., F.H.A. and H.N.S.; validation, G.H.A. and H.N.S.; formal analysis, F.H.A., G.H.A. and H.N.S.; fabrication, G.H.A., F.H.A. and H.N.S.; measurement, G.H.A., F.H.A. and H.N.S.; investigation, G.H.A. and H.N.S.; resources, F.H.A. and G.H.A.; data curation, F.H.A. and G.H.A.; writing--original draft preparation, F.H.A. and G.H.A.; writing--review and editing, F.H.A. and H.N.S.; visualization, F.H.A. and G.H.A.; supervision, H.N.S.; project administration, H.N.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Conflicts of Interest:** The authors declare no conflict of interest.