HP 8530A, Руководство по эксплуатации и программированию, Страница: 236 / 439

Time Domain RCS Measurements
Figure 13-6. Time Domain RCS Response Before and After Calibration
T arget Shadowing and T arget Scattering
RCS calibration can be less eective when removing range clutter behind the target zone . This
is because the target \shadows" a portion of the chamber directly behind itself. While the
target is in place , it may block some of the transmitted RF energy from the back wall of the
chamber . During the rst part of the calibration, the receiver measures the target plus the
background. The background measured has the shadow . Next, you remove the target and the
receiver measures just the background, however , the shadow no longer exists . This causes the
background subtraction to be less accurate . After calibration, a large back-wall reection may
reappear if the calibration target is large .
In addition, the target can scatter energy toward the walls and ceiling, which can cause
spurious responses that arrive after the target zone responses .
Shadowing and target scattering reduce the receiver's ability to observe small RCS responses
when large target responses are also present.
RCS Measurement Concepts
It is important to understand the following concepts when interpreting measured RCS
responses .
Masking
T arget masking is when the RCS response of one target scatterer will aect the measured
response of each subsequent scatterer . This occurs because the energy reected from (or
absorbed in) the rst scatterer never reaches those that are behind it. The result is that the
subsequent scatterers will present a lower RCS response than would occur if the rst scatterer
was not present.
Reverberations
Complex RCS targets will often have reverberations that occur within the target structures .
This causes their RCS Time Domain responses to be distributed (in time) beyond the calculated
target electrical length.
It is important to consider masking and reverberations when determining the best frequency
and Time Domain settings for viewing the target.
Introduction to Time Domain RCS and
Antenna Measurements
13-11