Effect of antenna directivity on spatial pattern of scatterers in urban macrocellular environment

When directional antennas are employed in the transmission link, the channel response is often obtained by applying a complex weight (antenna voltage pattern) to the waves distributing into/coming from different directions and is considered as a spatial filtering process. An important question is whether the antenna directivity has a substantial influence on the spatial pattern of scatterer distribution. As a consequence, allowing for a system-independent channel characterization may be implausible if the answer is yes. We present a systematic method to study the effect of antenna patterns on scatterer distribution in the multipath channel. The workhorse is the recently introduced semi-geometrically based statistical model and two heuristic rules, which establish the correspondence between geometric models and physical wave propagation processes. It is shown that the effect of a directional antenna is twofold. First, it alters the spatial distribution of scatterers by providing a different sample space for the random field; second, it distributes the signal components into the angles-of-departure or collects them from the angles-of-arrival by weighted combination.