A primary radar can be designed with stacked beams which can give a broad indication of the level band of a target; also, a specialist height finder primary radar, which scans verically in one direction at a time, could do the same thing. However, there is just no good reason for the expenditure on that sort of equipment in civil ATC, even if it could be obtained, and it would only be of very limited value as rather large minima for avoidance would have to be specified due to the radar tolerance and the aircraft's unknown intentions.
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