Experimental study of adaptive impedance matching in an indoor environment

In recent years, adaptive impedance matching (AIM) has been used to compensate for severe performance degradation in terminal antennas due to user proximity. In particular, user effect compensation is critical for multiple-input multiple-output (MIMO) terminals, to achieve high data rates. In this study, the AIM performance of a MIMO terminal is measured for three user scenarios at two locations in an indoor office environment, using real impedance tuners. It was established that AIM leads to MIMO capacity gains of up to 25%, corresponding to 2.2 dB of power gain. On the other hand, the insertion loss of the tuners was found to be about 0.3 dB for free-space conditions. These results suggest that AIM can offer significant net performance gains in practice. Moreover, we provide physical insight into the similar AIM results for the two measured locations, representing geometrical line-of-sight (LOS) and non-LOS links, respectively.