  The stationarity region, i.e., the area in which the statistics of a
propagation channel remain constant, is an important measure of the propagation
channel, and essential for efficient system design. This paper presents what is
to our knowledge the first extensive measurement campaign for measuring the
stationarity region of MIMO mm-wave channels. Using a novel 28 GHz phased-array
sounder with high phase stability, we present results in an urban microcell
LoS, and LOS to NLOS transition region scenario, for the stationarity region of
shadowing, power delay profile, and the angular power spectrum. A comparison to
results at cm-waves shows considerably reduced stationarity region size, which
has an important impact on system design.
