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

Abstract

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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.34\lambda \times 0.13\lambda \times 0.01\lambda $ </tex-math></inline-formula> at 4 GHz and the distance between two symmetrical elements is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.05\lambda $ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|S_{11}| \le -$ </tex-math></inline-formula> 10 dB, and an isolation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|S_{12}| \le -$ </tex-math></inline-formula> 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.