Adaptive impedance matching performance of MIMO terminals with different bandwidth and isolation properties in realistic user scenarios

Using the metric of channel capacity, three dual-antenna multiple-input multiple-output (MIMO) terminals with adaptive impedance matching were evaluated at LTE Band 13 in four different user scenarios using simulation. Each of the three terminals is equipped with a slot-monopole antenna and a planar inverted-F antenna (PIFA). The slot monopole is fixed at one edge of the chassis, whereas the location of the PIFA differs among the terminals to provide different bandwidth and isolation characteristics in free space (FS). The results show that adaptive matching leads to an average capacity gain of up to 24% at the center frequency, favoring the terminal with the smallest antenna bandwidth and the largest isolation. However, the maximum capacity gain from adaptive matching decreases to 15.7% when averaged over the entire system bandwidth. Moreover, the terminal with moderate antenna bandwidth and isolation offers the best overall absolute capacity performance under different user scenarios, indicating a design tradeoff. These results highlight important design considerations for MIMO terminals with adaptive impedance matching.