# GUI for Analysis of Parameters, Accurate Design and Optimization of Microstrip Filters
## 6 Results and Discussion
### Examples of Optimization  
**Example 1**.: _Filter with constant TL and maximum attenuation._  
As an example of the usefulness of optimization, a filter is initially designed with the characteristics outlined in Table 3.  
These parameters are entered into MicroStripOptim, then the \"Print Data\" button is clicked, resulting in a filter with the following characteristics:  
\[TL=88.9635\;\mathrm{mm},\;\;\;\;\;\;\max(L_{A})=28.5614\]  
To visualize the optimization tool, a simulation must first be run. To keep variations small, the following values are entered into the edit boxes:  
\[W_{Lmin}=0.2,\;\;\;W_{Lstep=0.02},\;\;\;W_{Lmax}=1\]  
\[W_{Cmin}=4,\;\;\;W_{Cstep=0.1},\;\;\;W_{Cmax}=10\]  
Then, click on the \"Simulate\" button. Once the simulation is complete, the value 88.9635 is entered into the \"TL const\" edit box, and the \"TL const\" button is clicked. As a result, a table of optimal values is generated, similar to the one in Figure 16. In this case, the optimal values for maximum attenuation are as follows:  
\[\max(L_{A})=30.3199\;\mathrm{dB},\;\;\;\;\;W_{C}=8.3\;\mathrm{mm},\;\;\;\;\;W_ {L}=0.2695\;\mathrm{mm}\]  
Figure 20: Scattering parameters measured for the PCB filter compared to MicroStripOptim simulation. (**a**) Transmission, \(|S_{21}|\): (**b**) reflection, \(|S_{11}|\). The response of the real filter, measured using a VNA, is very close to that predicted by MicroStripOptim, matching both the cutoff frequency and the maximum attenuation, which were the key design and optimization requirements initially proposed.  
\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) & \(f_{c}\) & 1 \\ Filter order & \(n\) & 5 \\ Source impedance (\(\Omega\)) & \(Z_{0}\) & 50 \\ Width of high impedance line (mm) & \(W_{L}\) & 0.4 \\ Width of low impedance line (mm) & \(W_{C}\) & 12 \\ \hline Filter type, Chebyshev—\(L_{Ar}=0.04321\) dB & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Parameters for designing _Filter 1_.  
Therefore, a filter with the same length as _Filter 1_ has been obtained, but with greater attenuation. From Figure 21, it can be observed that _Filter 2_ exhibits greater attenuation and was designed to have the same \(TL\).  
When designing a filter based on data like those in Table 3, it is not possible to know the total length (\(TL\)) beforehand. However, in MicroStripOptim, it is possible to design a filter in reverse, meaning that starting with a desired \(TL\), the values of \(W_{\text{C}}\) and \(W_{L}\) can be determined to meet the total length constraint. Since there may be multiple sets of values that satisfy this constraint, MicroStripOptim offers three options that optimize some specific parameters.  
If the simulation of the previous example has been executed, the edit boxes \"min(\(TL\))\" and \"max(\(TL\))\" are enabled. For the case of the previous example, the displayed values are as follows:  
\[\text{min}(TL)=81.4269,\quad\text{max}(TL)=127.5198\]  
Therefore, it is possible to obtain a filter with the desired length within these limits. If one enters  
\[TL\text{ const}=82\]  
by clicking the \"TL const\" button, the values to achieve a filter with \(TL=82\) mm, and optimal characteristics are obtained. In this case,  
\[\text{max}(L_{A})=34.5821\text{ dB},\quad\ W_{\text{C}}=9.7166\text{ mm},\quad\ W_{L}=0.2000\text{ mm}\]