Hardware and physical integration guideline PCR Sensor A111
Page 22 of 32
© 2022 by Acconeer
– All rights reserved
2022-03-08
Figure 23. 3D-printed examples of the hyperbolic and FZP lenses. The material used for printing is ABS plastic.
5.1 Focal distance
Radar measurement was done to characterize the focal point of the lens. The reflected power from a
fixed radar target was captured for different sensor-to-lens distance. The distance between the sensor
and target is to be in the far-field region, i.e. radar-to-target distance > 1m.
Figure 24 shows the gain variation of the integrated lens with the radome with respect to the free-space
scenario for the XM112 module (see Figure 23 for the prototype pictures). The maximum gain happens
at 7.5 mm distance for both lenses. Other maxima happen every half-of-a-wavelength (
𝜆
0
2
=
2.5 mm).
The gain oscillation is due to the constructive and non-constructive interference of the transmitted and
reflected waves between the lens surface and the sensor. The optimal placement can vary depending on
the radome design. The measured results for the XR112 radome (Figure 25) indicate that the maximum
gain happens at 8 mm distance. This can be due to the reflections from the radome side walls which can
create interference. Therefore, it is important for every radome design to characterize the focal distance
to find the optimum distance.
