An aircraft instrument landing system is disclosed wherein elevation angle measurements of an aircraft are derived by providing, in such system, a means for inhibiting an elevation swept beam of radiation from sweeping through ''''low'''' angles where significant multipath transmission is expected. Means are provided to vary the power in the transmitted beam of radiation in a predetermined manner as the beam is inhibited from sweeping. As a result the radiation received by the low flying aircraft is shaped in a way related to the shape of the received radiation expected without multipath transmission. Such arrangement enables the same aircraft receiver and processor to determine the elevation angles of both ''''high'''' and low flying aircraft without appreciable error.