# A Review on SIW and Its Applications to Microwave Components
## 11 SIW Power Divider/Combiner  
Power dividers are microwave passive components that receive input signals and provide several output signals with phase and amplitude characteristics [78; 79]. These components can be operated as power combiners by simply supplying signals into the divider output ports. The vector summation of the signals will appear as a single output at the divider's input port. Integrating power dividers/combiners (PDCs) and channel filters into a single component does not only reduce the physical footprint of the component, but also helps to significantly reduce losses. The reason is that integrated filtering PDCs [80; 81; 82] reduce the number of lossy connectors within a communication system, since the filter and the PDC exist as a single integrated device. It has been reported in the literature [78] that Y-junction-based power dividers provide a wider bandwidth of 25.2% when compared to T-junction [83]-based power dividers which provide 10.2% bandwidth.  
Various classes of SIW-based power divider/combiners have been reported in [78], including corporate (Tree), Series, multimode interference, half-mode SIW, Magic-T, radial cavity, Wilkinson and Gysel SIW power dividers. Filtering power dividers with tuneable and reconfigurable passbands has been proposed in [81], where tuneable resonators are employed to ensure the device can be used for reconfigurable applications. SIW-adjustable filtering power dividers have also been proposed in [82]. The design is based on multi-layer SIW and achieved both equal and unequal power division as shown in Figure 10. The design combines three similar slotline-microstrip transition structures containing two rectangular resonators, achieving the filtering power division responses as explained in [82]. A performance comparison of published works on SIW power dividers/combiners is given in Table 3.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & \multirow{2}{*}{\begin{tabular}{c} **\(f_{1}\)/\(f_{2}\)** \\ **(GHz)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Filtering** \\ **Order** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Isolation** \\ **(dB)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Insertion** \\ **Loss (dB)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Return** \\ **Loss (dB)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Dimension** \\ **(\(\lambda_{\mathbf{o}}\times\lambda_{\mathbf{o}}\))** \\ \end{tabular} } \\ \hline
[17] & 1.7/1.9 & 5 & \textgreater{}50 & 2.86/2.91 & 15/12 & - \\ \hline
[74] & 5/5.25 & 2 & \textgreater{}45 & 2.2/2.4 & 17/15 & 1.02 \(\times\) 2.08 \\ \hline
[74] & 5/5.25 & 2 & \textgreater{}40 & 1.8/1.5 & 16/18 & 1.02 \(\times\) 2.08 \\ \hline
[76] & 9.5/10.5 & 3 & \textgreater{}35 & 1.6/2.1 & 17/16 & 2.04 \(\times\) 0.65 \\ \hline
[77] & 10.5/13.5 & 3 & \textgreater{}42 & 0.9/1.4 & 14.4 & 2.14 \(\times\) 1.30 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Performance comparison of published works on SIW diplexers.  
Figure 9: Simulation and measurement responses of a tuneable SIW diplexer including the images of the fabricated filter component. Reprinted/adapted with permission from Ref. [77]. 2019, [PERSON] et al.