A novel compact multi-input multi-output (MIMO) antenna system with split-ring resonator (SRR), a popular metamaterial structure, is presented. The MIMO antenna system consists of SRRs as radiator elements arranged close to each other on a printed circuit board. We evaluate the antenna characteristics with a single and two SRR elements arranged within various sizes of area. We also analyze MIMO channel capacities of SRR elements by using radiation patterns. The obtained results confirm that the proposed MIMO antenna system can achieve the same channel capacity as a conventional MIMO antenna system but with a 30% smaller footprint area and is very suitable for compact wireless equipment in next-generation wireless systems.

A simple but efficient method for evaluating the channel capacity of 2×2 multiple-input multiple-output (MIMO) antenna systems is proposed. First, the channel capacity of a half-wavelength dipole array antenna is calculated using the Monte Carlo method by changing the incident-wave signal-to-noise power ratio, the power difference between two elements, and the correlation coefficient. Using the calculated results, a polynomial function is derived by multivariate regression analysis to estimate the channel capacity. The validity of the developed function is confirmed by comparing the channel capacity estimated by the developed function with that calculated by the Monte Carlo method using a MIMO array antenna operated under various scenarios, including antenna-human body electromagnetic interactions and radio-wave propagation environments, for future MIMO systems. The function is also validated by means of two experimental approaches: the use of radiation patterns measured in an anechoic chamber and the use of a spatial fading emulator that can create a two-dimensional fading environment.

In this paper, a new MIMO antenna for ultra-wide band (UWB) applications is designed and proposed. The proposed MIMO antenna consists of two single UWB antenna elements, one acts as a magnetic dipole while the other as an electric one, to reduce mutual coupling. In order to reduce further the mutual coupling, a copper stub is used to isolate the two antenna elements. The designed MIMO UWB antenna provides a broad operating bandwidth from 3.1GHz to 10.6GHz, while achieving low mutual coupling and VSWR ≤ 2. Various performance characteristics of the antenna such as radiation patterns, VSWR, and the maximal gain are thoroughly investigated by simulations and experiments.

In this paper, we present a weighted-polarization wearable multiple-input multiple-output (MIMO) antenna that is based on radio-frequency (RF) signal processing to realize ultra-high-speed and high-capacity mobile communications. The proposed antenna is comprised of three orthogonal dipoles, two of which can be selected according to a weight function in different usage scenarios. The weight function is determined by considering the variation in the cross-polarization power ratio (XPR) and the antenna inclination angle which depend on the radio-propagation environment and human motion. To confirm the suitability of the proposed antenna, we perform preliminary experiments to evaluate the channel capacity of a weighted-polarization wearable MIMO antenna with an arm-swinging dynamic phantom. The measured and analytical results are in good agreement, which verifies the effectiveness of the proposed antenna. We demonstrate that the proposed antenna is suitable for realizing gigabit mobile communications in future wearable MIMO applications.

A new structure to improve channel capacity of short-range MIMO is proposed. The proposed structure consists of back reflector and side reflector. FDTD simulation demonstrates a role of back reflector and side reflector. The back reflector increases all eigen values. The side reflector equalizes eigen value distribution. Consequently, the proposed structure enhances the channel capacity.

A neutralization line is internally added to a 770 MHz LTE-band miniature dual-antenna system to improve its antenna efficiency. The odd-mode antenna impedance simulations indicate that the position of the neutralization line along the radiating structure determines the operation frequency. Measurement results show that the line reduces the antenna coupling loss from -6 to -17 dB while improving the individual antenna efficiency from 42 to 65 percent at 770 MHz.

We address the issue of MIMO channel estimation with the aid of a priori temporal correlation statistics of the channel as well as the spatial correlation. The temporal correlations are incorporated to the estimation scheme by assuming the Gauss-Markov channel model. Under the MMSE criteria, the Kalman filter performs an iterative optimal estimation. To take advantage of the enhanced estimation capability, we focus on the problem of channel estimation from a partial channel measurement in the MIMO antenna selection system. We discuss the optimal training sequence design, and also the optimal antenna subset selection for channel measurement based on the statistics. In a highly correlated channel, the estimation works even when the measurements from some antenna elements are omitted at each fading block.