This paper presents the design and implementation of a quad-port aperture-coupled circularly polarized (CP) multiple-input multiple-output (MIMO) antenna, specifically fitted for X-band applications. The proposed antenna features an innovative design that uses a 90° power divider to excite two orthogonal modes. This is achieved through an aperture Line that is coupled to a patch via two unique, orthogonal dog-bone slots. A key element of the design is a parasitic patch, which incorporates a 9× 9 array of square pixel cells. This array is strategically included to simultaneously boost the antenna's gain and improve its axial ratio (AR) bandwidth. The problem of achieving high-performance CP MIMO in the X-band is addressed by the clever use of orthogonal mode excitation and the parasitic patch with its array. By carefully coupling the orthogonal modes, the antenna achieves circular polarization, which is critical for reducing multipath interference. The parasitic patch's role is to act as a director, enhancing the overall radiation characteristics without significantly increasing the antenna's size or complexity. This method allows for a compact design while maintaining high performance. The experimental and simulation results showed strong agreement. The antenna achieved an impressive impedance bandwidth (IBW) of 9.8-13 GHz (28%) and a 3-dB axial ratio bandwidth (ARBW) of 10.7-12.27 GHz (13.67%). Measured port isolations are below - 20 dB, with a gain of 7-8 dBic across the frequency band. The antenna's MIMO performance was excellent, as evidenced by a diversity gain (DG) of at least 9.99 dB, an envelope correlation coefficient (ECC) of 0.002 or less, and channel capacity loss (CCL) ≤ 0.2 bit/s/Hz, demonstrating its outstanding diversity capabilities. These results confirm the antenna's suitability for advanced X-band wireless technologies that require high data rates and robust connectivity.
Moharram et al. (Thu,) studied this question.