# Design of a Modified Compact Coupler with Unwanted Harmonics Suppression for L-Band Applications
## 4 Conclusions  
A new BLC is designed, simulated and fabricated in this paper. The T-shaped resonators, open stubs, cross-shaped resonators, stepped impedance resonators, and radial stubs are used in the designed coupler. A design procedure for the proposed BLC is pro \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Refs.**} & **Frequency** & **Insertion** & **Harmonic** & **Size** & **Advantage** & **Technique** \\  & **(GHz)** & **Loss (dB)** & **Suppression** & **Reduction** & **Advantage** & **Technique** \\ \hline
[11] & 1 & N/A & No & 60\% & Size reduction & Discontinuous microstrip lines \\ \hline
[12] & 2.4 & N/A & No & 70\% & Size Reduction & Quasi-lumped elements approach \\ \hline
[14] & 1 & 0.33 & No & 50\% & Size reduction & Step impedance transmission line \\ \hline
[15] & 0.836 & 0.9 & No & 74\% & Size reduction & Branch-line hybrid coupler \\ \hline
[16] & 2 & 0.36 & 2\(f_{0}\) & 72\% &
\begin{tabular}{c} Size reduction \\ Wideband \\ \end{tabular} & Slow wave \\ \hline
[18] & 2.45 & 0.45 & 2\(f_{0}\) to 5\(f_{0}\) & 55\% & \
\begin{tabular}{c} Harmonic \\ suppression \\ \end{tabular} &
\begin{tabular}{c} L-shaped \\ Open stubs \\ \end{tabular} \\ \hline
[19] & 0.9 & 0.3 & 2\(f_{0}\) to 4\(f_{0}\) & 64\% &
\begin{tabular}{c} Size reduction \\ Wideband \\ \end{tabular} & H-shaped microstrip line \\ \hline
[22] & 0.96 & 0.3 & 2\(f_{0}\) to 6\(f_{0}\) & 80\% & Size reduction & Eight open ended stubs \\ \hline
[23] & 1 & 0.3 & 2\(f_{0}\) and 3\(f_{0}\) & 63\% & Size reduction & Spiral open stubs \\ \hline
[24] & 2.1 & 0.9 & 2\(f_{0}\) and 3\(f_{0}\) & 63\% & Size reduction & Spiral T-shaped lines \\ \hline
[29] & 3.5 GHz & 0.5 & 2\(f_{0}\) & No & \
\begin{tabular}{c} Wideband \\ Filtering \\ \end{tabular} &
\begin{tabular}{c} Coupled lines \\ Open Stubs \\ \end{tabular} \\ \hline
[30] & 3.5 GHz & 0.5 & No & 35\% & Size reduction & Pi-Network \\ \hline
[31] & 0.9 & 0.76 & No & 36\% & \begin{tabular}{c} Size reduction \\ Flexible \\ \end{tabular} & \begin{tabular}{c} Open stub \\ Reader lines \\ \end{tabular} \\ \hline \begin{tabular}{c} This \\ work \\ \end{tabular} & 1 & 0.2 & 2\(f_{0}\) to 5\(f_{0}\) & 86\% & \
\begin{tabular}{c} Size reduction \\ harmonic \\ suppression \\ \end{tabular} &
\begin{tabular}{c} T-shaped resonators, Open stubs, \\ Step impedance, and Radial stubs \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance comparison between the proposed BLC and the recent ones. Figure 18: Photos of the fabricated BLC under test. vided and explained. The proposed resonator is analyzed, and the related equations are extracted. The microstrip realization of the proposed resonators are provided, which are finally incorporated in the typical BLC structure to form the proposed coupler. The designed BLC is very compact and has the harmonics suppression ability. The simulated results are confirmed by the measured results. The results show more than 86% size reduction of the proposed device, compared with the conventional one, which make the proposed device suitable for modern communication systems applications. Finally, the performance of the designed coupler is compared with several state-of-the-art couplers, which show the advantages of the proposed coupler. In the future work, the design process of the proposed coupler will be improved with the help of artificial intelligence and deep learning methods. Conceptualization, S.R. ([PERSON]), S.H. and S.R. ([PERSON]); methodology, S.R. ([PERSON]), A.H.F. and S.R. ([PERSON]); software, A.H.F. and S.R. ([PERSON]); validation, S.I.Y. ; formal analysis, S.I.Y., and S.R. ([PERSON]); investigation, S.R. ([PERSON]); resources, S.R. ([PERSON]), and S.H. ; writing--original draft preparation, S.I.Y. and S.R. ([PERSON]); writing--review and editing, S.R. ([PERSON]), and S.I.Y. ; visualization, S.R. ([PERSON]), and S.I.Y. ; supervision, S.R. ([PERSON]); project administration, All authors have read and agreed to the published version of the manuscript. This research received no external funding.