The Japanese would have been happy to incorporate radar into ships and early air warning. They lacked a sophisticated electronics industry to actually make the equipment. So too did the Germans; they could not have duplicated the proximity fuze in quantity even if they wanted to.
The Japanese existing industrial plant was stretched beyond its limits by the strain of war. They had no excess capacity to develop an electronics industry on the run.
Their ships had fairly decent radar after 1942. Why the IJ Army could incorporate that into AAA defense of homeland earlier is still another mystery.