a radiant energy detection system which allows angular location in bearing and elevation by using a simple detector element and a static mask preferably formed by a plzt strip between two intersecting polarizers . a control circuit operates the mask to provide a configuration having a transparent zone equal to n measurement quadrants and an opaque zone equal to the remaining 4 - n quadrants , and to bring about four successive operating states which are distinguished one from the next by an angular displacement of π / 2 radians around the optical axis . the control circuit operates further a switching circuit synchronously with the mask to connect the output of the detector successively to four reception channels each of which includes a high speed memory . a measuring circuit calculates the angular location from the four detected signal values stored in the memory .