# Multiport Single Element Mimo Antenna Systems: A Review
## 4 Multiport Single Element System
### Single Element Two-Ports MIMO Antenna System  
In [58], a novel single element MIMO antenna with dual-port based on isolated mode antenna technology (iMAT) was discussed. The phase and magnitude of the signal are changed due to few bends available in the crossover coupling structure connected to the single antenna radiating patch with two ports. To solve this issue and to attain good isolation, an I-shaped slot is etched at the ground plane which behaves as a LC filter. The iMAT concept was introduced in [59] also to achieve enhanced port-to-port isolation in which a U-shaped antenna with common radiator is designed and compared with two elements monopole antenna. In [60], a common radiator dual port antenna using iMAT for LTE band application was designed. A good isolation was achieved by etching a rectangular slot at the ground plane on the bottom side; which intersects with a T-shaped slot inserted at the radiating patch as shown in the Figure 5. The multiple slots and slits etched on the top patch and the ground layer reduces the mutual coupling and has a good bandwidth covering the LTE 2300; 2.4 GHz WLAN and LTE 2500 frequency bands. This proposed common radiator dual port antenna has a dimension of 48 \(\times\) 33.8 mm\({}^{2}\) suitable for mobile devices. The single element MIMO antenna system presented in [61], consists of two wideband monopole antennas which are orthogonally placed with a shared radiator and L-corner ground plane for the frequency bandwidth of 600 MHz from 2.3 to 2.9 GHz. As shown in Figure 6a; a parasitic element of chain-shaped structure with two sets of rings are etched on the top and bottom layer of the substrate. The position of rings is adjusted in such a way to generate a secondary current path; which can reduce the current distribution effects between the ports. This configuration provides good isolation between the ports and a return loss of less than \(-10\) dB is achieved. The two-port MIMO antenna system in [61] is presented for wireless access point indoor applications. In this design, two coplanar waveguide-fed ports which are perpendicular to each other are connected to a common radiator. On the same side of the substrate, an L-shaped ground plane is also etched as shown in Figure 6b to excite two orthogonally polarized modes [62]. Good isolation is obtained by introducing the chain-shape parasitic element (CSPE) between the ports. The total dimensions of the antenna structure are \(110\times 130\times 1.6\) mm\({}^{3}\). The stepped-cut technique at four corners is used by adjusting the shape of radiating patch to obtain the required bandwidth. The implemented antenna achieves a good isolation of around 15 dB, providing impedance bandwidth of 1.8 GHz from 0.9 GHz to 2.7 GHz [62]. A dual-port monopole antenna (64 \(\times\) 64 mm\({}^{2}\)) attached to a common radiator with a shape of circular disc with a radius of 20 mm was implemented in [63]. To excite from each port, a feed line 20 mm long and 3.5 mm wide is connected. To expand 10 dB input impedance bandwidth, a groove is inserted below each feeding line of the antenna as shown in Figure 7. To achieve a good isolation, a circular cut of radius R\({}_{\rm c}\) was etched in the ground plane, which restricts the current flowing between the two ports. Wide bandwidth of 2 GHz to 6 GHz is achieved with less than \(-15\) dB port-to-port isolation. Similarly,  
Figure 5: Fabricated prototype with T-shaped slot [60]. Figure 6: (**a**) Fabricated prototype with CPSE [61] (**b**) CPW-fed fabricated prototype with CPSE [62]. the dual-port microstrip antenna was presented in [64] which utilizes an external loop to attain good port-to-port isolation. An ACS-fed multiple-input-multiple output antenna presented in [65] operates from a frequency range of 3.1 to 10.6 GHz. A good isolation of more than 15 dB is achieved. The antenna design discussed in [66] is much smaller in size of 26 \(\times\) 26 mm\({}^{2}\) as compared to the antenna structure presented in [65].