Radars provide the benefit of line-of-sight target detection in low or no visibility situaitons. First you must choose the radar platform. Radome is more compact and open-array is bigger.
You can then narrow your selection by choosing either pulse radar, which is better at long range, or broadband radar which has instant-on capability and better short range resolution. Lastly select the radar power output, the larger the wattage the better the range and the target seperation.