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This letter experimentally investigates the performance of ultrawideband (UWB) radio technologies with multiple-input multiple-output (MIMO) antennas for body area network (BAN) applications. Effects of array spacing, antenna polarization, bandwidth and propagation on UWB-MIMO channel capacity are analyzed. The key finding here is to that in BAN the MIMO channel capacity is mainly determined by the power imbalance between subchannels compared to the sub channel correlation for both spatial array and polar array. For spatial array, the measured results show that the MIMO channel capacity is decreased when the array spacing is increased, despite the spatial correlation coefficient is decreased. This phenomenon is different from that in wide area networks (WAN) and wireless local area networks (WLAN). It is because that power difference among elements of the spatial array is significant in BAN short-range communications compared to that in WAN and WLAN. For polar array, the achievable channel capacity is lower than that of the spatial array in line-of-sight (LOS) conditions due to high cross-polarization discrimination. Furthermore, the MIMO capacity is slightly dependent on the environments due to dominance of human body effect. It is also found that the MIMO channel capacity decreased with frequency or bandwidth.