Signal path loss and propagation delay spread were measured at microwave fr
equencies of 3.35, 8.45, and 15.75 GHz along a straight quasi line-of-sight
(LOS) street in an urban environment under different traffic conditions: d
ay time and nighttime. Comparison between daytime and nighttime measurement
s reveals that the break points shift toward the base station because of th
e increase in the effective heights of the road and sidewalk; break points
were not seen during the daytime at a mobile antenna height (h(m)) of 1.6m.
According to the cumulative probabilities of the delay spreads during the
nighttime, frequency dependence is not clearly observed and the delay sprea
ds for h(m) = 1.6m were clearly larger than those for h(m) = 2.7 m. This is
because a lower h(m) results in stronger blocking of the LOS wave, as was
also observed during the daytime. The plot of path losses versus delay spre
ads is confirmed to be represented by an exponential curve. The exponential
coefficients during the daytime were observed to be greater than those dur
ing the nighttime. This indicates that a LOS wave is more likely to be bloc
ked during the daytime.