## 2 Design of MIMO Antenna
In MIMO antenna systems, mutual coupling between the individual antennas can degrade performance by interfering with signal transmission and reception. The CSRR can help to reduce mutual coupling between the antennas by creating isolation between them. It can act as a decoupling element, decreasing the coupling effects and improving the isolation between the antennas. The insertion of a CSRR can alter the radiation pattern of the patch antenna. The CSRR can affect the current distribution and electric field distribution on the patch, leading to changes in the radiation characteristics. Properly designed CSRR structures can be used to shape the radiation pattern and improve the antenna's performance in terms of gain, directivity, and radiation efficiency. MIMO systems often benefit from polarization diversity, where different antennas are designed to transmit and receive signals with different polarizations. The CSRR can help to enhance the polarization diversity of the patch antenna by modifying its polarization properties. By carefully designing the CSRR, it is possible to achieve improved polarization isolation and better performance in terms of cross-polarization discrimination. The incorporation of a defective ground structure (DGS) in a antenna can have several effects on its performance, as follows: Cross-polarization refers to the undesired reception or transmission of signals with a polarization orthogonal to the desired polarization. DGSs can help to suppress cross-polarization in MIMO antennas. By introducing appropriate DGS patterns or slots in the ground plane, the radiation characteristics and polarization properties of the antenna can be controlled, leading to improved polarization isolation and reduced cross-polarization. DGSs can be used to shape and control the radiation pattern of MIMO antennas. By incorporating specific DGSs, such as slots or patches, in the ground plane, the current distribution and electromagnetic field distribution on the antenna can be manipulated. This enables control over the antenna's radiation pattern, beam steering, and directivity, which can be advantageous in MIMO systems to optimize coverage, increase gain, or mitigate interference. DGSs can help to mitigate interference from external sources or neighboring antennas by introducing appropriate DGSs. Using structures in the ground plane, such as slots or fractal patterns, it is possible to suppress the effects of nearby interfering signals or electromagnetic noise, improving the signal quality and overall performance of the MIMO system. The antenna design technique is analyzed in four essential parts in order to explain the working concept of the planned MIMO antenna. Table 1 shows the four structures of the proposed design. DS-1 consists of two hexagonal-shaped MIMO structures along with one circular-shaped portion engraved in the patch area. Two slits are also placed on the outer side of the hexagonal-shaped patch region. Two arrays of lines and one plane region are available in the diffracted ground region. DS-2 has two hexagonal-shaped MIMO structures without a circular shape. Two slits are also placed on the outer side of the hexagonal-shaped patch region. Two arrays of lines and one plane region are available in the diffracted ground region. DS-3 has two hexagonal-shaped MIMO structures with a circular-shaped portion engraved in the patch area. There are not any slits in the outer place of the hexagonal-shaped patch region. Two arrays of lines and one plane region are available in the diffracted ground region. DS-4 has two hexagonal-shaped MIMO structures with one circular-shaped portion engraved in the patch area. In addition, there are slots available in the outer place of the hexagonal-shaped patch region. The ground region is simple without array lines. The DS is a technique