Designing 2-port and 4-port multiple-input multiple-output antennas with frequency-selective surfaces for sub-8 GHz

Spectrum lower than 8 GHz still continues to be important in applications such as 5G and beyond, wireless communication systems with regard to achieving wide coverage area and higher data rates. Nevertheless, some limitations have been observed in terms of limited bandwidth, low gain, and mutual coupling in the case of Microstrip Patch Antennas (MPAs) in Multiple-Input Multiple-Output (MIMO). This study develops miniaturized 2-port and 4-port MIMO MPAs in combination with an innovative frequency-selective surface (FSS). A modified patch antenna with a square-ring defected ground structure, orthogonal configuration of radiators, and cross-coupling networks is developed. The superstrate of FSS includes square unit cells having circular and cross-shaped slots to improve directivity and radiation efficiency without compromising impedance matching. The designed antennas exhibit bandwidth ranging from 4.9 to 8.1 GHz (2-port MIMO) and 4.69 to 7.885 GHz (4-port MIMO) with a maximum gain of 5.8 and 11.9 dB, respectively. Excellent performance measures have been observed in the form of envelope correlation coefficient less than 0.002, diversity gain more than 9.99 dB, channel capacity loss below 0.03 bit/s/Hz, and overall reflection coefficient equal to −13 dB. The suggested antenna structure represents a reliable and easy-to-fabricate approach to sub-8 GHz wireless communications as well as 5G mid-band communications.