In this paper, a simple novel technique to self-isolate multiple-input-multiple-output (MIMO) antenna array elements for mm-wave applications is proposed. MIMO antenna arrays with inter-element separation of 0.2 mm (0.023λ at 35 GHz) and measured high isolation (>50 dB) are presented. Several rigorously optimized slots of different shapes, positions, and dimensions are etched on the radiating patch to enhance the inter-element isolation within 28-37.5 GHz impedance bandwidth. The surface current distributions, parametric analysis, and two MIMO array configurations are employed to validate the proposed self-isolation technique. The novel mm-wave antenna exhibits high impedance bandwidth (>29%), high isolation (>50dB), high efficiency (>90%), high gain (>9.5 dB), and low envelope correlation coefficient (<0.005) throughout the desired bandwidth. Two configurations of the MIMO antenna arrays are fabricated and measured to validate the simulation outcomes. To the best of the authors’ knowledge, the presented design is the first to exhibit such wideband isolation improvement without any external decoupling structure at the mm-wave frequency range.

In this paper, a novel beam steerable 2.4 GHz MIMO antenna array is proposed based on the Yagi-Uda principle. The antenna consists of two co-axially excited patch radiators with modified ground plane. A conducting strip with an integrated PIN diode is optimally placed between the patch radiators to act as a director or a reflector to steer the main beam by an angle of +/- 60◦. For all switching modes, the MIMO antenna demonstrates an average gain and efficiency of 5 dB and 92%, respectively, at the resonance frequency of 2.4 GHz. Reduced envelope correlation coefficient in one switching mode exhibited 17 dB improvement in mutual isolation. The simulated results agreed well with measured data. This simple, low-cost, efficient, and mutually isolated antenna array can be very useful in MIMO WLAN applications.