Operating the R&S
QAR
R&S
®
QAR
43
User Manual 1178.7200.02 ─ 09
5.1.3.2
Reflection Measurement
The reflection measurement determines the amount of energy that is being reflected by
the DUT. This energy does not pass through the radome and contributes to perfor-
mance degradation as a result. Reflected signals reduce the performance of the radar
and can even interfere with the received signals, leading to effects as described in
application note
. Areas with a high reflection can have various causes, for
example material defects, undesired interaction between several layers of materials,
excessive amount of certain materials, or foreign objects.
The R&S
QAR achieves spatially resolved reflection measurements of a DUT by link-
ing the information collected by the distributed transmit and receive antennas in a
coherent operation. The resulting millimeter wave image allows for an intuitive evalua-
tion of the DUTs reflection behavior.
Measurement results
The application shows the results of the spatially resolved reflection measurement as a
millimeter wave image with a linear scale from 10
% to 100
%. The x- and y-axis show
the dimensions of the image in mm (300
mm x 300
mm by default). By default, the
image is a grayscale image. Small values, represented by dark areas, correspond to a
low reflection, high values, represented by bright areas, correspond to a high reflection.
A color map next to the image shows the levels that correspond to each shade of color.
In addition to the image, the mean reflection and the standard deviation of the reflec-
tion are calculated as numeric results. Both values are shown under the millimeter
wave image in logarithmic units (dB) and as a percentage, with 100
% representing a
maximum reflection of 0
dB.
The application calculates the numeric results over a certain area of the complete milli-
meter wave image. The evaluation area is indicated by a mask that is superimposed
on the image. You can customize the size and form of this mask to analyze certain
areas in more detail. For more information about working with the mask, see
The mean reflection indicates the radar transparency of the DUT. The lower the mean
reflection, the better the radar transparency of the DUT. A higher mean reflection
results in beam refraction, increased transmission loss and standing waves between
the DUT and the radar sensor. For optimal radar compatibility, the DUT's mean reflec-
tion has to be minimized.
The reflection's standard deviation indicates the homogeneity of the DUT. Inhomogene-
ous DUTs alter the incident wave's phase fronts, cause angle errors, blind spots and
increased side lobes. For optimal radar compatibility, the DUT's reflection standard
deviation has to be minimized.
5.1.3.3
Transmission Measurement
Because the incident signal is split in a reflected and a transmitted part, it is of interest
to measure not only the reflection but also the transmission properties.
Measuring the transmitted signal, requires the optional transmitter module that is loca-
ted behind the DUT (on the DUT table). The transmitter uses 64 discrete frequency
Radome Measurements
