**2. Antenna Design**

A compact four-port MIMO antenna is designed and fabricated on a FR4 substrate with thickness (*t*) = 1.6 mm, loss tangent (*tanδ*) = 0.025, and dielectric constant (*εr*) = 4.4. Figure 1 illustrates the geometry of the proposed antenna, and the optimum parameters related to the proposed antenna design are listed in Table 1. A simple decoupling structure is implemented in the ground plane to obtain good isolation. CST Microwave Studio has been used for simulation purposes to design and analyze the antenna parameters. The total dimensions of the MIMO antenna are 40 mm × 40 mm (~0.59λ × 0.59λ at center frequency of 4.45 GHz). The design stages are demonstrated in the subsequent sections.


**Table 1.** Antenna dimensions of the proposed design (mm).

**Figure 1.** Structure and dimensions of proposed 4 × 4 MIMO antenna.
