Antenna Space Diversity And Polarization Mismatch In Wideband 60GHz-Millimeter-Wave Wireless System

Recently, the evolving fourth generation (4G) mobile communication systems are expected projected to solve still-remaining problems of third generationsystems and to provide a wide variety of new services, from high quality voice to high-definition video to high-data-rate wireless channels. As the spectrum in the low microwave frequencies goes congested, moving to the largely unused spectrum at millimeter wave frequencies will avoid the interference from the other radio systems and have potential to achieve a high speed wireless communication system. Of the millimeter-wave (MMW) frequencies, particularly interested is the 60-GHz band,which is provided as an unlicensed band in many countries such as Japan (59-66 GHz), United States (57-64 GHz), and Europe (57-66 GHz). This is the largest contiguous block of radio spectrum ever allocated. Immense research and development on the millimeter-wave devices, circuits, antennas, and modules have been done in recently years.This paper presents a study on the fading behavior in wideband 60GHz-Millimeter-wave (MMW) wireless system. The evaluation is carried out based on a two-ray propagation model, with considering the large propagation loss of the multi-reflected waves other than the first reflected wave at 60GHz-millimeter-wave. The study focuses on the strong fading effect due to the large variation of antenna location compared to the short wavelength (about 5mm) and the wide frequency range (about 9GHz) in such MMW wireless system. The influence of the polarization mismatch of antenna is also investigated. To reduce the fading, we employ the technique of space diversity by introducing two or more antennas in receiving side. We perform an optimization of the locations (heights) for these antennas. From the simulation results, we obtain some optimal heights with which the fading effect can be reduced in less than 3dB. The simulation results also reveal how the polarization mismatch, in two different cases of antenna rotations, influences the system performance, and how space diversity reduce the fading as well. The antenna used in simulation is a planar patch antenna which is considered suitable for portable wireless handset. The radiation pattern is obtained from electromagnetic simulation. This paper demonstrates that by employing multiple antennas with optimized antenna locations can significantly reduce the fading for the 60GHz-MMW wireless system.