  Comparisons of outdoor Urban Microcell (UMi) large-scale path loss models,
root mean square (RMS) delay spreads (DS), angular spreads (AS), and the number
of spatial beams for extensive measurements performed at 28, 38, 73, and 142
GHz are presented in this letter. Measurement campaigns were conducted from
2011-2020 in downtown Austin, Texas, Manhattan (New York City), and Brooklyn,
New York with communication ranges up to 930 m. Key similarities and
differences in outdoor wireless channels are observed when comparing the
channel statistics across a wide range of frequencies from millimeter-wave to
sub-THz bands. Path loss exponents (PLEs) are remarkably similar over all
measured frequencies, when referenced to the first meter free space path loss,
and the RMS DS and AS decrease as frequency increases. The similar PLEs from
millimeter-wave to THz frequencies imply that spacing between cellular base
stations will not have to change as carrier frequencies increase towards THz,
since wider bandwidth channels at sub-THz or THz carrier frequencies will cover
similar distances because antenna gains increase quadratically with increasing
frequency when the physical antenna area remain constant.
