This paper presents wideband measurements in a laboratory environment. These measurements provide further evidence in support of the previously published hypothesis that the clusters within the Saleh-Valenzuela propagation model are manifestations of antenna impulse responses. The issue caused by frequency variations of the antenna radiation pattern of wideband antennas and by the selection of antenna type are discussed. It is shown that due to limited movement in target applications of extremely wideband systems, the variation of antenna impulse responses due to the change of mutual antenna position does not significantly change. Thus, the deterministic nature of the antenna impulse responses can be exploited in the design of more efficient receivers.