# Generation of Sparse Antennas and Scatterers Based on Optimal Current Grid Approximation
## 2 Review of Approaches for Reducing Mass and Surface of Various Antenna Structures Using the OCGA
After the comparative analysis, these works provide conclusions and recommendations about the following:  
* The approach that provides better reduction in antenna mass, surface, and cost for subsequent modeling (approach for reduction);
* The approach that provides the best antenna characteristics (approach for characteristics);
* The frequency at which the sparse structure is created is based on the current distribution at the frequency that has the best characteristics (current distribution for sparse structure);  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Antenna** & \(f\), **GHz** & **GEET, \%** & **Prototype** & **Original WG** & **Sparse After OCCA** & **Sparse After** \\ \hline \hline \multirow{4}{*}{Reflector} & \multirow{4}{*}{3.4-3.7} & \multirow{4}{*}{30} & \multirow{4}{*}{**Prototype**} & \multirow{4}{*}{**Original WG**} & \multirow{4}{*}{**Sparse After OCCA**} & \multirow{4}{*}{**Sparse After EOCGA**}  
The frequency at which the antenna characteristics of the sparse structure are obtained is least dependent on the GEET value (frequency for characteristics). The sparse WG structures presented in Table 1 demonstrate the accuracy of various approaches. OCGA excluded the wires with normalized smaller current magnitudes than a given GEET value and obtained the corresponding sparse WG structures. However, it can be seen that some free wires appear in the sparse structures after OCGA. Therefore, EOCGA eliminated them while NCOCGA recovered the necessary wires to connect them to the WG structure. The sparse structures obtained after EOCGA and NCOCGA had no free wires. This confirms the correct performance of the modernized algorithms, since they can be applied to various antenna structures. The results summarized in Table 3 show that the greatest value of antenna mass and surface reduction and simulation cost is usually obtained after OCGA and EOCGA, and the smallest value of the maximum antenna characteristic difference when compared with the results obtained for the original structure is usually obtained for the sparse structure after NCOCGA. Comparing the sparse structures obtained based on the current distribution at different frequencies, it can be noticed that virtually all works recommend that the sparse structures are generated based on the current distribution at the lowest or center frequency in the operating frequency range. Moreover, when comparing the antenna characteristics obtained at different frequencies for sparse structures, the antenna characteristics obtained at the highest frequency in the operating frequency range are stable and less dependent on the GEET value than at other frequencies. All the results obtained after applying OCGA and its modifications on different antenna structures operating at different frequencies demonstrate the effectiveness of these approaches in creating sparse structures. The sparse antenna structures have lower mass, surface, and modeling cost than the original structure, while the antenna characteristics are maintained. Sparse antenna structures can be used to fulfill various requirements, such as in IoT devices or space applications where there are severe specifications on antenna mass