Channel capacity enhancement of MIMO system based on phase shift lens antenna structure

Abstract

The objective of this paper is to improve MIMO (Multiple-In Multiple-Out) channel capacity of wireless communication system by reducing the mutual coupling with the application of lens. The lens application on integrated antenna system differs from conventional antenna lens, which increases the antenna gain. The proposed lens changes the phase component of antenna's radiation pattern and this change induces the reduction of envelop correlation correlation. Therefore, the channel capacity of MIMO system can be increased. First, the possibility of channel capacity improvement is explained with the phase variation of radiation pattern caused by application of lens. The proposed lens, which is modeled as a plane shape, has a refractive index corresponding to its permittivity. Conventional antenna lens acts as a convex lens, which focuses on the direction of electromagnetic wave's propagation. However, the proposed lens makes the variation of wavelength and velocity caused by a refractive index. When the electromagnetic wave penetrates the lens, the attenuation and phase variation of signal are generated. This change means that the existence of lens induces the variation of channel characteristics in view of channel environment. Also, in view of antenna system, the variation of radiation pattern occurs with respect to magnitude and phase signal. In this thesis, with the application of lens, the appearance of phase variation was derived analytically based on the wave theory of electromagnetic wave, and the analysis result has been compared with the simulated results. Second, the antenna structure which is applied to MIMO system has been proposed and the possibility of channel capacity enhancement based on the usage of lens has been verified. The channel capacity enhancement induced by lens application is based on the enhancement of pattern diversity gain, therefore the proper antenna structure is required to get pattern diversity gain. In this thesis, the integrated antenna which can support MIMO system based on pattern diversity gain has been proposed and its frequency characteristics has been verified. Also, to show the effectiveness of lens application for pattern diversity gain enhancement, according to the lens usage, the mutual coupling and correlation reduction has been checked. In addition, based on this performance enhancement, the channel capacity has been compared and it was shown that the proposed system shows the best performance than the conventional system. At last, we verified the antenna diversity enhancement of the array antenna structure. When the array system is applied, the conventionally proposed pattern antenna and new application of lens show the decreased antenna diversity performance. To improve the performance, first we verified the reason why the array structure decreases the antenna diversity. Also, to solve the performance degradation, the improved lens structure with linearly slanted concave lens is designed by the required phase distribution derived from the phase distribution equation of planar lens. The proper antenna design for lens application has been implemented. From the above simulation results, the integrated antenna array system is constructed and simulated. The effectiveness of revised antenna and lens structure is verified in view of channel capacity.