Experiments with Compact Antenna Arrays for MIMO Radio Communications
  The problem addressed in this study is how to design and test compact antenna arrays for portable Mulitple-Input Multiple-Output (MIMO) transceivers. Mutual coupling in an antenna array affects signal correlation and array radiation efficiency - both of which have dramatic consequences for MIMO channel capacity. Mutual coupling becomes more pronounced as array aperture shrinks and is therefore a critical issue in compact array design. Two novel compact arrays are designed and fabricated for use in MIMO enabled mobile devices. These arrays are extremely compact yet demonstrate acceptable mutual coupling and radiation efficiency because of the MIMO-specific criteria used during their design. An experimental methodology is presented for fair and meaningful characterization of MIMO arrays by field trial. This methodology addresses the issue of capacity normalization and quantifies how well an antenna array's radiation pattern interfaces with multipath propagation. Results are presented from an extensive measurement campaign in which a true MIMO transceiver testbed is outfitted with compact arrays and dipole arrays of various sizes. A comprehensive and fair comparison is made between the compact arrays and dipole arrays in a variety of indoor propagation scenarios. Design recommendations for compact MIMO arrays are given. 
D. W. Browne, M. Manteghi, M. P. Fitz, Y. Rahmat-Samii