HP 8530A, Руководство по эксплуатации и программированию, Страница: 235 / 439

Time Domain RCS Measurements
The frequency response error term accounts for these dierences , as well as other \non-RCS"
measurement eects . T o the extent that these measurement errors are repeatable , they can be
quantied (during calibration) and their eects removed from the measured data.
RCS Calibration makes two separate measurements:
It measures the reference target.
It measures the empty chamber .
The order of measurement does not aect calibration. After these two measurements are
nished, the HP 8530A:
Subtracts the chamber response (background) from the reference target response .
Divides the result by the theoretical response of the reference target to give the frequency
response error term.
The empty chamber response is then used as the isolation error term.
If the target mount changes , simply install the new target mount (with calibration turned ON)
and perform an \Update Isolation" calibration. Refer to the RCS Calibration section for more
details .
RCS Calibration is performed on Frequency Domain data, and therefore aects both Frequency
Domain and Time Domain RCS responses . Of particular interest in this section are the eects of
calibration on the Time Domain responses (see Figure 13-6).
Horizontal Axis: T arget Zone Shift. The location of the reference target along the time axis
will change when RCS calibration is turned ON. With calibration OFF , the location (in time) of
the target zone is determined by:
The distance between the range antennas and the test target.
T o a lesser extent, by the electrical dierences between the test and reference paths . Since
calibration is OFF , frequency response errors still aect the measurement.
When the receiver turns calibration ON, it moves the target zone to zero seconds (because of
the phase calibration performed on the Frequency Domain data).
V ertical Axis: Clutter Removal and Reference Level Shift. RCS calibration will also apply
background subtraction to remove much of the range clutter from the Time Domain RCS
measurement. This makes the target response more visible .
After calibration, the receiver adjusts the overall reference level to display the target
amplitude in dBsm.
13-10 Introduction to Time Domain RCS and
Antenna Measurements