Design of 8-port compact hybrid fractal UWB MIMO antenna with a conjoined reflector-ground integration for isolation improvement

Abstract

In this article, a compact 8-port UWB MIMO antenna was proposed to operate from (2.5–24) GHz with 162.2% impedance bandwidth. To achieve space diversity, i.e., maximum antenna elements accomodated in a premium foot-print, each radiating pairs are designed with self-similar hybrid geometry and oriented in side-by-side orthogonal configuration. The substrate corners are cut-out for maximum free space radiation and volumetric reduction. The isolation improvement mechanism is achieved by conjoining an annular reflector at top with the ground plane via metallic vias. The metal vias magnetically couple reflector and the ground plane into a connected topology. The annular reflector has dual-purpose, firstly, the contra-cyclic surface current symmetry improves the lower mode impedance matching and secondly, port-isolation is achieved (>22 dB) by electrically self-neutralize near-field radiated currents due to contra-rotational E-field NULL distributions. The antenna MIMO diversity performances show good attributes for indoor and outdoor wireless environments. To validate, a prototype antenna of size 48 mm × 48 mm (0.4λ×0.4λ,λ = operating wavelength at 2.5 GHz) was fabricated and measured. The simulated and measured results has good agreements to be explored in UWB MIMO systems, microwave telemetry, tracking and RF doppler sensor applications.