Compact wideband MIMO antenna for 4G WI-MAX, WLAN and UWB applications

摘要

This article proposes a compact wideband MIMO antenna. The antenna comprises of two identical modified P shaped monopole radiators, spatially oriented at 180 degrees to each other with side to side spacing of 0.075 lambda(o), where lambda(o) is the wavelength corresponding to the lowest operating frequency. To design a compact antenna, a semicircular monopole with a rectangular strip is designed instead of a circular monopole. This P shaped monopole antenna offers same impedance bandwidth with 50% size reduction. To enhance the impedance bandwidth of the antenna, the effective current path length is increased by introducing two semi-circular slots in P shaped monopole antenna. To achieve the desired impedance bandwidth of 2.5-12 GHz, the rectangular strip is corrugated on both sides in the slotted P shaped monopole. Triangular slots and meshed metal strip are introduced in the ground plane to achieve high mutual coupling over wideband. The triangular slots act as variable length capacitance and exhibits wide band notch characteristics. A meshed metal strip acts as decoupling structure for the surface current emerging from the surface waves and also act as reflector for space waves. Those bands which are not rejected by triangular slots, are notched by meshed metal strips. Thus by employing both triangular slots and meshed metal strip, isolation >20 dB is achieved over 2.5-12 GHz. The proposed antenna is a novel design which has smaller dimensions and still offers isolation >20 dB over a wider impedance bandwidth of 2.5 GHz to 12 GHz as compared to state of art antenna structures reported in literature. The band stop characteristics of proposed isolation techniques are analyzed by suspended stripline method. Mutual coupling reduction is also analyzed with the help of vector surface current density and magnetic field distribution. The proposed structure has compact dimensions of 0.25 lambda(0) x 0.241 lambda(0). The fabricated prototype antenna exhibits envelope correlation coefficient (ECC) >0.02, diversity gain >9.5 dB and stable radiation patterns. The antenna is suitable for 4G WI-MAX, WLAN and UWB applications. (C) 2018 Elsevier GmbH. All rights reserved.