# Wire-Grid and Sparse MoM Antennas: Past Evolution, Present Implementation, and Future Possibilities
## 5 Wire-Grid Sparse Antennas  
### Overview  
The history of computer development goes back more than 60 years. Over the years, technology has improved rapidly, resulting in the evolution of computers from large mainframes of collective use to today's superpowered workstations. During this time, computer technology has become a tool for many people. Therefore, the development of computer technology explains the intensive work undertaken to create new methods in all branches of science, focused on the computer. Modern CAD involves the use of computers,  
Figure 4: Example of an antenna in the form of a grid of wires as a transformable antenna with gilded wire mesh (mounted on Luch 5A, Luch 5B, and Luch 5V) [259]. Figure 3: Example of an antenna made of composite materials [258]. and they develop in the direction of comprehensive automation in all stages of the product life cycle. This situation also emphasizes the problem of creating new methods of design and construction, and mathematical and software algorithms for solving various scientific and engineering problems [260]. Thus, for example, applied electrodynamics includes the tasks of designing antennas and antenna arrays, synthesizing planar multilayer absorbers and multilayer dielectric structures, developing frequency-selective surfaces and various electromagnetic devices, etc. To solve electromagnetic field problems, there are various approaches that are reduced to analytical or numerical solutions of the corresponding integral or differential equations in the frequency or time domain. Analytical solutions are accurate, however they are obtained only for a limited range of simple structures. Thus, the use of a thin-wire approximation allows us to analyze various antennas [261]. In this case, such an approximation can be extended to the wire grid, for example, to design lens antennas [262; 263; 264; 265; 266; 267; 268; 269]. Microstrip [270; 271], reflective [272; 273], and indoor antennas for mobile communications [274] can also be represented in the form of a wire grid. In addition, the thin-wire approximation is applicable to solving scattering problems. Thus, for example, the work [275] presents an analysis of the reflection transmission of a plane wave at oblique incidence on a wire grid parallel to the plane interface of two homogeneous dielectrics. In this analysis, the space on both sides of the interface is represented in the form of transmission lines. The use of numerical methods allows for the analysis of antennas of arbitrary configurations [276]. Application of these methods allows moving beyond continuous functions to their discrete analogues, thus making a problem solvable. As a result, the problem is reduced to finding an approximate solution of [PERSON]'s equations. A distinctive feature of numerical methods is the partitioning (discretizing) of the geometric model into small cells (grid construction) [277]. With this feature, both partial differential equations (DE) and integral equations (IE) can be solved in the time domain. PDEs can be solved using the transmission line matrix method (TLM) and the FDTD as well as the finite element time domain (FEMTD). IEs, in turn, can be solved using the partial-element equivalent circuit method (PEEC). In FD, the solutions can be either in the high-frequency (HF) or low-frequency (LF) domain. In LF, the equations can be solved with DE and IE. The former can be solved using the FEM, while the latter can be solved using MoM and PEEC. To find a solution in the HF domain, asymptotic methods based on physical and geometrical optics as well as diffraction theory are used. The peculiarities and the results of MoM application in the analysis of wire-grid objects are presented in many works as the solution of scattering tasks and antenna tasks. Thus, the use of the collocation method (a special case of MoM) to solve the scattering problem by wire objects is considered in [278]. To increase the accuracy of calculations, additional boundary conditions are imposed on the segments of each wire.