# GUI for Analysis of Parameters, Accurate Design and Optimization of Microstrip Filters
## 6 Results and Discussion
### Filter Analysis with MicroStripOptim  
In this section, the main results obtained with the developed app are described. We explain the function of each button embedded in the GUI. In order to illustrate one case of study, the design data inputs shown in Table 2 are introduced in the edit-boxes in the upper-left side of the GUI. The first button of the GUI (see Figure 6), \"Scattering\" takes the data for filter design (values in Table 2) from the edit-boxes of the GUI. Then, it computes the widths and lengths of the filter lines. Afterwards, the program applies the steps of Section 2.3 in order to produce the plot of the scattering parameters. The result of this function is shown in two plots. The first plot (see Figure 7a) corresponds to the scattering parameters \(\mid S_{11}\mid\) and \(\mid S_{21}\mid\) of the filter generated using the data of Table 2. The second plot, Figure 7b, shows the derivative of the attenuation, \(L^{\prime}_{A}\), given in dB/GHz. The second button of the GUI is \"Print Data\". This function takes the data of Table 2 from the edit-boxes in the GUI and retrieves a table with many information about the calculated filter. Figure 8 is an example of the tables retrieved. The table on the left gives \begin{table}
\begin{tabular}{l c c} \hline \hline
**Parameter** & **Label** & **Value** \\ \hline Dielectric constant & \(\varepsilon_{r}\) & 4.4 \\ Height of the substrate (mm) & \(h\) & 1.27 \\ Cutoff frequency (GHz) & \(f_{c}\) & 2 \\ Filter order & \(n\) & 7 \\ Source impedance (\(\Omega\)) & \(Z_{0}\) & 50 \\ Width of high impedance line (mm) & \(W_{L}\) & 0.6 \\ Width of low impedance line (mm) & \(W_{C}\) & 6.183 \\ \hline Filter type, Chebyshev - \(L_{Ar}=0.01\) dB & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values introduced to design a filter. Figure 6: Graphical User Interface for analyzing microstrip low pass filters. information about the filter, like the filter parameters, source impedance, \(Z_{0}\), limits for \(W_{L}\) and \(W_{C}\), total length, width of the filter, the maximum attenuation and the derivative of maximum attenuation. The table on the right side of Figure 8 shows the widths and lengths of all the lines of the microstrip, as well as their inductance and capacitance equivalent values. The third button is \"Find Limits\". This button runs the Algorithm 3 to find the minimum value for \(W_{C}\) and the maximum value for \(W_{L}\), named as \(W_{Cmin}\) and \(W_{Lmax}\), respectively. The first action of this button is to compute \(W_{Cmin}\) and \(W_{Lmax}\) for the filter type and filter order, \(n\), set in the edit-boxes (variables shown in Table 1). Then, the program displays these values in the edit-boxes \(W_{Lmax}\) and \(W_{Cmin}\) of the GUI. Following the computation of \(W_{Lmax}\) and \(W_{Cmin}\) for the selected filter, the software computes the same parameters for all other filter architectures supported in this version of the program. The results are plotted all together, including the width of the source impedance line, \(W_{0}\), in Figure 9. From this figure some conclusions can be drawn. As a first conclusion, it can be said that, in general, as the order of the filter increases, the limits move away from the value \(W_{0}\). The only exception is in the limits of \(W_{C}\) for the Butterworth--MAXIMALLY FLAT filter, which has its minimum value in the fifth order. On the other hand, the second conclusion appointed is that the value of \(W_{Lmax}\), in the case of the Butterworth 0.5 dB and 3 dB filters, is very low, making them infeasible, thus, these two filters are discarded in the next analysis. From the limit values for the different filters and orders, further inspection can be made. For example, the total physical length, \(TL\), of the filter varies with the widths of \(W_{C}\) and \(W_{L}\), observing that the minimum \(TL\) for some filters is obtained with \(W_{Lmin}\) and \(W_{Cmax}\), whereas the maximum \(TL\) is obtained with \(W_{Lmax}\) and \(W_{Cmin}\).