I have tested the directivity of 5.8GHz HFS-DC06H radar sensor and found it to be 360 degrees, although I was expecting it to be 180 degrees because of the back metal shield on the antenna PCB. See the attached images for the sensor and radiation pattern from some Chinese website.

I want to have the directivity of 180 degrees instead of 360 degrees. Is there is some DIY shielding which I can use to limit the radiation pattern?