Edinburgh Napier University

  In this paper, single-element and MIMO microstrip antenna with two pairs of unequal slits is proposed as a circularly polarized antenna with negligible back radiation for 5G mid-band handsets. The unequal pairs of slits are engraved on the antenna patch to guarantee the presence of the circular polarization (CP). The proximity-coupled feeding technique is used to excite the proposed microstrip antenna in order to provide larger antenna-10dB bandwidth which approaches to 10.8% (3.48-3.87 GHz). A novel analysis technique is proposed in this paper that is based on demonstrating the 3D axial ratio pattern in order to generate CP in the broadside direction without affecting the structure of the ground plane which ensures a weak back radiation. The 3dB axial ratio bandwidth (ARBW) is found to be equal to 4.1% extended along the range (3.58-3.73 GHz). To make the design more compatible with the 5G mid-band handsets, the 2x2 MIMO structure of the proposed antenna with reduced mutual coupling (less than-20dB) is also presented in this work. The simulation and measured results are in good agreement, and both verify the CP characteristics and the weak back radiation of the proposed antenna.