The Causal Nexus Between Different Feed Networks and Defected Ground Structures in Multi-Port MIMO Antennas  
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Markhausen Institut, 01067 Dresden, Germany; [EMAIL_ADDRESS] (S.K. ); [EMAIL_ADDRESS] (P.S. ); [EMAIL_ADDRESS] (G.P.F)  
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antenna isolation include neutralization lines [36; 37; 38; 39], decoupling networks [40; 41; 42; 43] and parasitic structures [44; 45; 46; 47]. Their operating mechanisms involve the introduction of an extra coupling current that ultimately cancels out the original coupling current between the antenna elements. However, these solutions degrade some of the key performance metrics of MIMO antennas. Composite media created to exhibit distinctive electromagnetic properties, such as metamaterials [48; 49; 50; 51; 52; 53] and EBG structures [54; 55; 56; 57], are noteworthy solutions that can achieve high isolation while maintaining the desired overall performance of MIMO antennas. Nonetheless, these alternatives necessitate complex layouts and high fabrication costs. On the contrary, the DGS represents a cost-effective and easy-to-fabricate solution for a wide range of applications [58; 59; 60; 61]. It has previously been demonstrated that determining a feeding mechanism for microstrip antennas is a crucial choice because it has an immediate impact on the device's overall performance [62; 63; 64]. The four most utilized feed procedures include coaxial probe [65; 66; 67], microstrip line [68; 69; 70], proximity-coupled [71; 72; 73], and aperture-coupled [74; 75; 76]. However, the impact of different feed networks on the performance of MIMO antennas integrated with DGSs has never been considered. Consequently, this research aimed to determine the causal relationships between different feed networks and DGS-based MIMO antennas. The sub-6 GHz spectrum of 5G networks, currently at the cutting edge of wireless technology, was selected as the desired operating frequency band for this study [77; 78; 79]. Descriptively, 5.8 GHz was the intended \(f_{c}\) for both radiating and DGS elements. Rectangular patches were taken into consideration as the MIMO antenna's radiating elements owing to their lowered design complexity, and noteworthy antenna key performance indicators that have been determined in the past by many researchers [63; 80]. In addition, the SCSRR was chosen as the DGS configuration in recognition of their noteworthy advantages, which are covered in further detail in the next section [81; 82; 83]. Note that the sole objective of these MIMO antenna specifications and their operational spectrum is a starting point to begin the detailed investigations. Overall, this study is significant, since it provides a clear road map to determine the antenna performance enhancement capabilities, design complexity, cost analysis, and feasibility for integration with diverse technologies. The major contributions of this paper are summarized below:  
1. A thorough review with succinct summary on the antenna feeding techniques and DGS layouts. 2. Modeling of the dual element rectangular patch antenna and SCSRR-based DGS for operation in the sub-6 GHz spectrum. 3. The four (one at a time) feed procedures, namely, coaxial probe, microstrip line, proximity-coupled, and aperture-coupled, were applied to a dual port antenna integrated with an SCSRR-based DGS for the simulation studies of antenna as well as diversity parameters. 4. Validation of simulation studies by fabrication and measurements of four dual-port antennas integrated with an SCSRR-based DGS and fed via four distinct feed methods. 5. Comparison of different feed networks of SCSRR-based DGS MIMO antennas in terms of BW, peak isolation, and peak gain.