(A) study on design of MIMO antennas with different polarizations and performance evaluation in reverberation chamber for millimeter-wave 5G communications

Abstract

Millimeter-wave (mmWave) frequency bands have been popularly considered for 5G wireless communications in industry and academia. The mmWave band enables the use of a very wide spectrum to provide higher data rates. An antenna array has been required to compensate a severe propagation loss in using the mmWave frequency band for mobile communications. The mmWave 5G channel model should ensure that the channel states such as line-of-sight (LOS) or non-line-of-sight (NLOS) and the channel realizations change as a function of time, antenna position and polarization in all propagation scenarios. A study on design of multiple-input multiple-output (MIMO) antennas with different polarizations and performance evaluation in reverberation chamber (RC) is presented at 28 GHz band for mmWave 5G communications in this thesis. First of all, various antenna arrays based on a substrate-integrated-waveguide (SIW) technique for mmWave handset devices are presented. In terms of antenna polarizations and configuration, eight types of antenna arrays providing 1×4 and 1×8 array sizes with horizontal polarization (HP), vertical polarization (VP), left-handed circular polarization (LHCP), and right-handed circular polarization (RHCP) are proposed. The proposed antenna arrays meet the desired performance for the mmWave 5G communication such as low-cost, broadband performance, and high gain characteristic. Based on the eight types of the antenna arrays with different polarizations, twelve cases of 2×2 MIMO antennas are proposed. The channel performance of the proposed MIMO antennas is evaluated in the RC by using a 28 GHz channel sounder. Furthermore, an experimental validation for mmWave channel measurement is investigated to verify the channel performance according to the different configurations and polarizations. The MIMO measurements are fulfilled in the RC without and with absorbers to provide an ideal and relatively real wireless environment. To clarify the channel performance for each case, a wideband channel capacity is calculated from the measured results. Additionally, a tapered slot antenna (TSA) array with calibration couplers is investigated for mmWave beam-steering applications. Each component of the proposed TSA array such as the antenna element, power divider, directional coupler, and transition structure is introduced in detail. The measurement results of the proposed TSA array are also presented to verify the antenna performance.