## 5 Benchmarking  
The effects of four popular feed networks--coaxial probe, microstrip line, proximity-coupled, and aperture-coupled feed--on a traditional patch antenna with a full ground plane were thoroughly investigated in [102]. The results of this research indicated that the proximity coupled feed approach stands out in achieving a wide bandwidth, and all feeding methods' gain values showed some variation, with the highest gain deviation value being \(\approx\)1.7 dBi. However, our results in Table 8 indicate that all feeding techniques have a relatively different effect on the behavior of MIMO antennas integrated with SCSRR-based DGS. A variation of behavior arises from the integrated DGS and distinct feeding network. As it is widely known, an integrated DGS structure significantly affects the impedance-matching circuit in several ways such as modifying the effective permittivity and permeability of the substrate. Depending on the geometry, the DGS structure acts as an inductive and capacitive, resulting in input impedance changes in the antenna. The proposed SCSRR-based DGS induces electromagnetic force that generates a current flow within the metallic rings and gaps, producing a balanced inductive-capacitive effect. Accordingly, the selection of a feeding technique for the MIMO antenna is also crucial since it affects key performance parameters like radiation efficiency, BW, and impedance matching. Therefore, to design a high-performance MIMO antenna integrated with DGS, two essential criteria come to the forefront, such as choosing a proper feeding network and a suitable DGS-shaped device, which have direct impacts on the impedance matching circuit.  
Figure 41: Simulated and measured radiation patterns of aperture-coupled feed MIMO antenna with SCSRR-based DGS: (**a**) E-plane; (**b**) H-plane.  
Figure 40: Simulated and measured radiation patterns of proximity coupled feed MIMO antenna with SCSRR-based DGS: (**a**) E-plane; (**b**) H-plane.  
Particularly, both proximity-coupled and aperture-coupled feed methods are advantageous for wideband applications, and all feeding methods offer similar gain values. Furthermore, our research adds light on the isolation values. In [103], a microstrip line fed MIMO antenna with SCSRR-based DGS was proposed for isolation enhancement. However, the design was limited to achieving a maximum isolation of 27 dB. Similarly, several other MIMO antenna designs for isolation enhancement have focused on SCSRR-inspired DGS with a microstrip line feed, as evident in [104; 105; 106]. Our research demonstrates that a coaxial probe feed technique is capable of attaining relatively high peak isolation (48 dB see in Figure 38) without complicating the MIMO antenna design due to their feed network and DGS-shape being compatible and providing good impedance matching. Table 9 presents a comparison of simulation results between the feed networks of the reference antennas and our recommended configurations. Our simulations and measurements confirm that integrating a precisely designed DGS, coupled with optimized feed network configurations, enhances key performance parameters of the MIMO antenna, as demonstrated in the proposed coaxial probe-fed MIMO antenna. It may be concluded that the choice of antenna feed type has received less attention over the years. Thus, our study provides valuable insights to assist future researchers in choosing the appropriate feed type according to their intended applications, and it constitutes the work's original contribution.