Page 394 - Fundamentals of Radar Signal Processing

near-in clutter echoes. These “off” periods represent the blind zones in range. In

this example, the first target is close enough to the radar that its echo is 50
percent eclipsed because it arrives during the near-in clutter interval. The third
echo is also 50 percent eclipsed because the target is far enough away that a
portion of the echo is received during transmission of the next pulse. The middle
echo is not eclipsed.
Blind zones in range and Doppler collectively combine to form a two-

dimensional blind zone map as shown in Fig. 5.27. Targets that fall within a
range blind zone are undetectable no matter what their Doppler shift. Targets
that fall within a Doppler blind zone are undetectable at any range. The spacing
of the blind zones in both dimensions is determined by the PRF of the radar. If
the PRF is increased, the Doppler blind zones spread further apart but the range
blind zones contract to become closer together. This observation leads to the
idea of using CPI-to-CPI stagger in combination with an “M out of N” detection

logic to maximize the combinations of range and Doppler shift at which targets
can be detected.