A Dual-Band Quad-Port Circularly Polarized MIMO Antenna Based on a Modified Jerusalem-Cross Absorber for Wireless Communication Systems

A modified Jerusalem-cross absorber (MJCA) based on resistors is presented to minimize mutual coupling at two independent bands of a very compact quad-port multiple-input-multiple-output (MIMO) antenna. The double E-shaped radiating element features sectoral slots, enabling the antenna to function at two distinct frequencies: a lower band (LB) of 6.5 GHz and an upper band of 8.5 GHz. These slots also facilitate the conversion of linear to circular polarization, adding to the antenna's versatility and performance capabilities. The MJCA, composed of four resistors placed at right angles to each other with 150 Omega lumped resistances, provides an absorbance rate of more than 90%, and reflectivity tends to zero at both operating bands. The single antenna is modified into a 4 x 4 MIMO antenna, with all elements tilted up to 15 degrees to improve impedance matching and increase isolation to some extent. Moreover, a 2 x 2 array of MCJA is placed on top of the MIMO antenna at a certain height, further enhancing isolation up to -35 and -25 dB at the 6.4-6.8 and 8.3-8.6 GHz frequency bands, respectively. In addition, it also improves the bandwidth of the MIMO antenna to up to 100 MHz at the LB. A detailed equivalent circuit design procedure is developed to understand the operating principles better. The designed MIMO antenna's performance with diverse parameters is also analyzed. The fabrication and measurement of the MIMO antenna validate the simulation results and demonstrate a good agreement between them. The proposed MIMO antenna is a competitive candidate for various modern wireless communication systems, including satellite communication, remote sensing, navigation systems, radar systems, and medical applications.