A Compact SD-QMSIW-Based Self-Diplexing MIMO Antenna Using Two Modified L-Shaped Slots as Radiators for IoT Applications

This article proposes a low-profile, compact dual-band shielded quarter-mode substrate integrated waveguide (SD-QMSIW) based self-diplexing multiple-input-multiple-output (MIMO) antenna for Internet of Things (IoT) heterogeneous networks (HetNets). The antenna is designed for Worldwide Interoperability for Microwave Access (WiMAX) and wireless LAN (WLAN) applications across the IoT environment. The MIMO configuration comprises two identical radiating self-diplexing antenna (SDA) elements arranged orthogonally. Each of these proposed SDA elements utilizes two modified L-shaped slots positioned on the upper conducting plane of the SD-QMSIW cavity, facilitating the construction of a miniaturized single-element SDA. This single-element SDA is driven by two separate 50- $\Omega $ microstrip feed lines, enabling radiation at two distinct resonance frequencies, 3.5 and 5.8 GHz, with better isolation greater than 37 dB between the ports. The proposed SDA design method is exceedingly flexible, allowing us to independently construct the antenna at two distinct frequency bands. Furthermore, a lumped circuit model of the proposed SDA element is anticipated to validate the designed single element SDA structure in conjunction with electromagnetic (EM) simulations of the antenna prototype. Moreover, the MIMO configuration of the proposed SDA element enables compact antenna circuit size of $0.29\lambda _{g}^{2}$ , isolation greater than 19 dB between the various ports of each SDA element, along with gains of 4.54 and 5.47 dBi at ports resonating at two identical frequencies. The outcomes of MIMO antenna features involving envelope correlation coefficient (ECC), effective diversity gain (EDG), and multiplexing efficiency (MUX) have been evaluated and found to be satisfactory for the proposed SD-QMSIW-based self-diplexing MIMO antenna.