An innovative fractal monopole MIMO antenna for modern 5G applications

Proposed in this paper is the design of an innovative and compact antenna array which based on four radiating elements for multi-input multi-output (MIMO) antenna applications used in 5G communication systems. The radiating elements are fractal curves excited using an open-circuited feedline through a coplanar waveguide (CPW). The feedline is electromagnetically coupled to the inside edge of the radiating element. The array’s impedance bandwidth is enhanced by inserting a ground structure composed of low–high-low impedance between the radiating elements. The low-impedance section of the ground is a staircase structure that is inclined at an angle to follow the input feedline. This inter-radiating element essentially suppresses near-field radiation between adjacent radiators. A band reject filter based on a composite right/left hand (CRLH) structure is mounted at the back side of the antenna array to reduce mutual coupling between the antenna elements by choking surface wave propagations that can otherwise degrade the radiation performance of the array antenna. The CRLH structure is based on the Hilbert fractal geometry, and it was designed to act like a stop band filter over the desired frequency bands. The proposed antenna array was fabricated and tested. It covers the frequency bands in the range from 2 to 3 GHz, 3.4–3.9 GHz, and 4.4–5.2 GHz. The array has a maximum gain of 6.2dBi at 3.8 GHz and coupling isolation better than -20 dB. The envelope correlation coefficient of the antenna array is within the acceptable limit. There is good agreement between the simulated and measured results