A Compact Quadruple-Band Circular Polarized MIMO Antenna With Low Mutual Coupling

This brief presents a compact multiband multiple input multiple output (MIMO) antenna, where two robot-character-shaped patches are closely positioned on the top of the substrate for circular polarization. The dimensions of the proposed MIMO antenna are
$0.34\lambda \times 0.13\lambda \times 0.01\lambda $
at 4 GHz and the distance between two symmetrical elements is
$0.05\lambda $
mm. The robot-character-shaped patch generates four different frequency bands of 3.85-4.25 GHz, 4.95-5.1 GHz, 6.94-7.35 GHz, and 8-8.3 GHz. The simulation and measurement results show that the designed antenna has better S-parameters
$|S_{11}| \le -$
10 dB, and an isolation of
$|S_{12}| \le -$
25 dB resulting from the irregular parasitic element to reduce mutual coupling, an axial ratio (AR) of no more than 3 dB, radiation pattern, total gain, and efficiency over all operating bands when compared to the existing two-port MIMO antennas. MIMO antennas diversity characteristics are also calculated to evaluate the proposed antennas performance. The proposed antenna is a good contender for 5G pioneer band, 5 GHz WLAN band, and satellite communication applications concomitantly.