A Quadrilateral Self-Isolated Wideband MIMO SIW Fractal Koch Snowflake Slot Antenna Array for Ka-Band Communications

This work proposes a new approach to design a quadrilateral self-isolated multiple-input–multiple-output (MIMO) antenna configuration operating for reliable $Ka$ -band communications. The proposed design utilizes a single-layer substrate integrated waveguide (SIW) fractal Koch snowflake (FKS) slot antenna array. The main focus is on achieving wideband characteristics and self-isolation among antennas without using any additional isolation circuits. The method is described to obtain the wideband performance of the SIW FKS slot antenna array fed with a grounded coplanar waveguide (GCPW). The radiation performance of single-element and quadrilateral elements is analyzed. The simulation and measurement results demonstrate that the MIMO antenna elements exhibit a bandwidth of 27.1–32.4 GHz (17.8%) and peak gain of 8.3 dBi at 28 GHz. The achieved isolation levels are greater than 23 dB (simulated) and 20 dB (measured), with a self-isolation structure. Furthermore, this work extended to calculate diversity characteristics of proposed MIMO, such as the envelope correlation coefficient ( $\text {ECC} \lt 0.005$ ), mean effective gain ratio ( $\text {MEG} \lt 1.1$ ), diversity gain ( $\text {DG}\lt 9.9$ dB), and channel capacity loss ( $\text {CCL}\lt 0.3$ bits/s/Hz). These results validate that the proposed MIMO antenna design is performing satisfactorily. The fabricated prototype measurement results are validated with simulation results.