Design and Simulation of Single and $2\times 2$ MIMO Circularly Polarized Patch Antennas with a Pair of Chip Resistors for 5G Applications

This paper presents single microstrip antenna and MIMO structure with two equal length pairs of slits and two chip resistors as an antenna with circular polarization (CP) and broadside radiation for 5G mid-band portable devices. The two chip resistors are placed at a pre-calculated positions on a certain pair of slits to provide a slit length different from the other pair of slits in order to guarantee the presence of the CP. To obtain larger impedance bandwidth, the antenna is excited using the proximity-coupled feeding that results in simulated impedance bandwidth equal to 13.8% (3.38-3.88 GHz) with realized gain larger than 2dB along the operational band. By manipulating the antenna three-dimensional axial ratio pattern, the orientation of the CP is adjusted toward the broadside direction without defecting the antenna ground plane so that the back radiation of the proposed antenna is minimized. This process guarantees negligible undesired back radiation. The simulated 3dB axial ratio bandwidth (ARBW) in the broadside direction is equal to 4.65% (3.57-3.74 GHz). Moreover, $2\times 2$ MIMO antenna structure, whose mutual coupling has values less than −20 dB, is also proposed in this paper to provide an antenna that is more convenient for the 5G handsets.