Q-Band MIMO Antennas with Circular Polarization for Spatial and Polarization Diversity

The present work proposes three MIMO antennas with different configurations for the future applications of wireless communications in the Q-band of the frequency to realize both spatial and polarization diversities. A circularly polarized (CP) printed antenna operating over two frequency bands at 37.8 and 50 GHz is utilized as a single element to construct the proposed MIMO antennas. Two-element MIMO antenna systems arranged in two configurations, side-by-side and face-to-face, are proposed to achieve spatial diversity. Also, a four-element MIMO antenna system is designed to achieve polarization diversity in addition to spatial diversity. The proposed MIMO antenna systems are designed with the aid of the CST simulator. The three MIMO antennas are fabricated and their performance is experimentally evaluated regarding the circular polarization, impedance matching, antenna gain, envelope correlation coefficient (ECC), and diversity gain (DG). The experimental results for the single-element as well as the MIMO antennas come in good agreement with simulation results showing high performance. Both the numerical and experimental investigations reveal that the mutual coupling between any two ports of the proposed MIMO antennas is below \(-25 {\text{dB}}\) $-25\text{dB}$ . Also, for any two ports it is shown that the ECC is below \(1\times {10}^{-7}\) $1\times {10}^{-7}$ and the diversity gain is higher than \(9.99\) $9.99$ . The impedance matching bandwidths (for \(\left|{S}_{11}\right|<-10 {\text{dB}}\) $\left|S_{11}\right|<-10\text{dB}$ ) are shown to be \(1.53\) $1.53$ and \(1.88\) $1.88$ GHz at \(37.8\) $37.8$ and \(50\mathrm{ GHz}\) $50\mathrm{GHz}$ , respectively, and the corresponding 3-dB axial ratio bandwidths are \(700\) $700$ and \(130\mathrm{ MHz}\) $130\mathrm{MHz}$ , respectively.