User's Manual

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MSAN-00X
AP97 K-Band Miniature Doppler Transceiver Module
Application Note
V1.00
7. Placing the module in enclosure
When AP97 sensor module is housed in an enclosure, it is important to ensure that the performance of
the module is not significantly degraded by the presence of the enclosure.
A suitable material with both lower dielectric constant and lower loss tangent (that is ABS) is preferred.
Microwaves penetrate through plastic material without significant loss as long as it does not have direct
contact with the antenna patch surface. In comparison, metal results in full reflection while water results
in significant absorption of microwaves. Therefore it is important not to place any metallic material in
front of the antenna.
Ideally, surface of the enclosure in front of the antenna should be flat. Curved surface introduces beam
pattern distortion, both main beam and side-lobes.
It is also important for user to note that the selection of the enclosure thickness, and the spacing in
between from the antenna patch surface, is in relation to the wavelength of the microwave signal and the
dielectric constant of the enclosure material. For ABS material that has a dielectric constant of between
2.5 to 3.5, the recommended spacing is approximately 6mm, and the recommended thickness is between
3 to 4mm.
User is advised to fine-tune the spacing between the antenna and the enclosure in accordance to their
application for optimum performance as depicted in figure 5.
Figure 4: Optimizing thickness and clearance for ABS placed in front of AP97 sensor module.
3 ~ 4mm
ABS enclosure
Antenna side
6mm (requires fine-tuning)
AP97
unit