Compact circularly polarized 2 and 4 port multiple input multiple output antennas with bandstop filter isolation technique: Compact circularly polarized 2 and 4 port multiple input multiple output antennas

Reduction of mutual coupling in the radiating elements of multiple input multiple output (MIMO) antenna is always an issue and a big challenge for antenna researchers. To address this issue of mutual coupling reduction, an effective method of decoupling has been proposed in this paper. Here, a bandstop filter based isolation technique has been introduced to limit the mutual coupling in each element of the MIMO antenna. A 2 port and a 4 port MIMO antenna have been designed with the proposed decoupling technique, and it is found that the decoupling technique successfully achieves isolation of more than 30 dB for both antennas. In addition to achieving high isolation, the designed MIMO antennas are also made circularly polarized to overcome poor mismatch, lower directive gain, and signal to noise problems in wireless communication. The antenna performance is observed in simulation and verified with measurements. Simulated and measured results show that the 2 port antenna exhibits a 10 dB impedance bandwidth of 5.26 % (2.78–2.93 GHz) and a 3 dB axial ratio bandwidth of 13.08 % (2.65–3.02 GHz), while those for the 4 port antenna are 2.46 % (2.41–2.47 GHz) and 13.10 % (2.36–2.69 GHz). The 2 port antenna supports a peak gain of 3.27 dBi with a maximum efficiency of 85.11 %, while the 4 port antenna successfully increases the gain to 6.49 dBi but decreases the maximum efficiency to 80.54 %. Both the MIMO antennas show excellent diversity performance in terms of envelope correlation coefficient (ECC), Directive Gain (DG), Total active reflection coefficient (TARC), channel capacity loss (CCL), and mean effective gain (MEG) ratio. Both the structures achieve ECC of less than 0.006, DG of more than 9.9 dB, TARC of less than −19.84071 dB, CCL of less than 0.00179 bits/s/Hz, and MEG of less than −0.00577 dB in measurements. The overall dimensions of 2 port and 4 port antennas are limited to 44×22×1.6mm³ and 44×52×1.6mm³, respectively. These characteristics of the proposed antennas make them suitable for use in wireless high-speed communications.