Abstract-Using the metric actual diversity gain (ADG), diversity performance is investigated for a compact mobile terminal prototype with two internal, triple frequency band antennas in four different cases of user interaction. ADG is presented as a preferred alternative to apparent diversity gain and effective diversity gain. Absorption due to user proximity causes degradation and imbalance in mean effective gain of the antennas over the frequency bands, contributing to a degradation in diversity performance. However, user-induced changes in the antenna patterns cause a decrease in correlation in the low frequency band, which facilitates increased diversity gain. The study reveals that a significant net diversity gain, i.e., ADG of 5-8 dB compared to a single antenna prototype, can be achieved using multiband antennas in the proximity of a user, even at low frequencies for antennas with high mutual coupling.

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Link to publicationCitation for published version (APA): Vasilev, I., Plicanic, V., & Lau, B. K. (2016). Impact of antenna design on MIMO performance for compact terminals with adaptive impedance matching. IEEE Transactions on Antennas and Propagation, 64(4), 1454-1465. DOI: 10.1109/TAP.2016 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal 1  Abstract-Using the metrics of channel capacity and multiplexing efficiency, the adaptive impedance matching (AIM) performances of two multiple-input multiple-output (MIMO) terminals with different antenna designs were evaluated and compared. The evaluation was performed in LTE Band 18 Downlink (860-875 MHz) under realistic usage conditions of two measured user handgrips and simulated propagation channels with different angular spreads (ASs). The results provide potential performance gains from AIM based on realistic MIMO terminal prototypes, and the underlying mechanisms by which the gains were achieved, which can serve as antenna and AIM circuit design guidelines. In particular, the evaluation revealed that ideal uncoupled AIM networks can increase the capacity by up to 52% relative to 50 ohm terminations. However, the observed gains depend heavily on the antenna design, the user scenario and the channel's angular spread. For example, the wideband design in different user cases experienced capacity gain of 4-9% from AIM in uniform 3D channels, in contrast to the 1.3-44% gain seen in a conventional narrowband design. In nonuniform channels with small ASs, the AIM gain for different mean incident angles depends on the absolute mean effective gain (MEG) and the change in correlation due to AIM; In cases where AIM has little impact on correlation, the mean incident angles with high AIM gains were close to those with high MEGs.Index Terms-MIMO systems, impedance matching, antenna measurements, handset antennas and multipath channels.